During the introductory sequence, the car is seen driving up the Italian side of the Grand St. Bernard pass and then driving down the same side again, whereas it's evidently intended that it crosses the pass.
In the scene where the mafia wreck the first E-Type Jaguar, Charlie says to the mafia boss "You just cost him his no claims bonus!" No claims bonus is a British term and would not have been understood by an American audience. It was re-dubbed as "You just cost him his insurance bonus!"
The car used when Charlie came out of prison was supposed to have been stolen from the Pakistani Ambassador (as Charlie points out to Lorna when they're in it and he shows her the flag). As a member of the Commonwealth (which they still were in 1969 although they left three years later), Pakistan did not have an Ambassador in London, but a High Commissioner.
The bonnet of Charlie's Aston Martin is hinged at the nose of the car. When the car gets thrown off the cliff, the hinges are near the cockpit. This is because the car which was thrown off the cliff was in fact a Lancia Flavia convertible
When the Minis are getting lined up on the autostrada to enter the bus, the road is a two-lane road with a solid line between lanes, but in a close up of Croker we see a three-lane road with a dashed lane markings.
The opening drive during the credits sequence was clearly shot in the same rugged, lifeless landscape used for the final sequence with the bus. As the credits end, the camera cuts to Beckerman in the car, then when we cut to the exterior again, suddenly we are surrounded by greenery and a completely different landscape, as the car approaches the tunnel.
When the plow comes out of the tunnel with the Miura on its fork, you can see the arm of the driver leaning on the door. Later, when the plow starts pushing the car off the rocks, it's empty. Yet we see something which looks like a body fall down the cliff when the car is pushed over the edge.
When Croker et al confront the Mafia on the mountain road and have their fast cars destroyed, the red Jaguar is already damaged. Even before the truck hits it, you can see that the left-hand headlight is missing.
At the end, as the coach swings round over the edge, you see a full vapour trail from a plane. Moments later, a shot of the stationery coach from the same camera shows the plane and a partial trail. Presumably the coach was positioned first, then swung back onto land, and the film reversed in the film to make it seem like it was swinging off, rather than on.
When the minis drive up onto the roof of the aircraft museum and split. The Red mini goes off to the left (White goes straight on) and Blue goes off to the right. After the police car stops and the officer gets out, the minis start driving towards him but the Red and Blue minis have somehow swapped places.
Whilst Mini Coopers were used in the escape sequences - identified by twin petrol cap fillers on each rear flank - the cars thrown out of the coach are standard Minis with only one petrol cap on the rear flank.
When the car flips off the carrier and crushes the police car, the gumball light diffuser pops off and lands intact on the ground. Later in a close shot the diffuser is shown to be cracked off with the base still attached to the car.
The truck used to ram the door in Turin is from the Fiat factory, but the purple car that falls off the back is a Farina-designed Austin Cambridge. It's a rusty old Austin, too, not a shiny new one. The boot interior is dirty and a different color to the exterior.
During the opening sequence, when the mobster steps on the glasses of the victim, the mobster's car and the bulldozer treads are shown as parallel to the stone retaining wall. However, the bulldozer is shown both before and after this scene as being perpendicular to the stone retaining wall.
When the Coopers are being prepped in the garage prior to the Job, one car has the rear end jacked up. The mechanic says something is wrong with the differential. Swapping the diff in a Mini (a front-wheel drive car) requires the removal of the engine and gearbox which are at the front, not the back.
However, this could be an intentional 'mistake' left in by the writers/film-makers. When this film was made front wheel drive cars were not as commonplace in the UK as they are today and most mechanics where used to working on the standard rear wheel driven cars. Asking an inexperienced mechanic to change the diff on a Mini was apparently a common practical joke/jape. The film maker may have also been implying that one of Charlie's mechanics wasn't up to scratch as there are various other gags in the film referring to their ineptitude (i.e. "you're only supposed to blow the bloody doors off!").
The Minis are driven up ramps and onto a moving bus. Since the road they are travelling on is virtually deserted and the police are no longer in pursuit, they could easily pull over to drive the Minis onto the bus without the need for the dangerous maneuver.
Gold weighs 19300 kg/m³ - so the mentioned and stolen half ton (be it metric or not makes no big difference) of gold would be a cube with a side length of about one foot. However, the amount of gold shown looks more like one cubic meter.
The Chinese characters on the plane from China are basically nonsense: "China Government Fly". They are also traditional characters, which were replaced by simplified characters in the 1950's in Mainland China.
During the heist, Charlie shouts "Now! Now! Go! Go! Go!" in order to get the minibus to force its way into the traffic jam. But in the long shot showing the minibus pulling out after the bullion van, there is clearly a huge gap left by patiently waiting cars which allows the minibus to complete the manoeuvre. This would never have happened in a real traffic jam, particularly in Italy.
When the Mini Coopers drive around the church where the wedding is occurring, the red car comes from the right and then the white car comes from the left. Finally, the blue car comes from the right and at least six different tire tracks can be seen on the steps coming from the right, indicating this scene was shot several times.
When the Lamborghini Miura is rammed by the snow plow and gets thrown off the cliff into the water, the engine lid opens and the engine is not there. This is
because the Lamborghini used for this accident was already a wreck when it "met" with the snow plow.
At the beginning of the film, just after the Lamborghini enters the tunnel we see a brief shot of the Bulldozer as the car's tyres screech. If you look very carefully you can see the Lamborghini has already been secured to the front of the machine. After the explosion the Bulldozer reverses out of the tunnel mouth, there is a rope leading from the front of the wheel arch down the main beam of the Bulldozer blade.
The goof item below may give away important plot points.
At the end of the movie since the coach hasn't actually fallen over the cliff, there is no need to panic. As soon as everybody moves as far as possible from the cliff's edge (without disembarking), their weight will stabilize the vehicle enough for one man to start fetching the gold. The more he fetches, the safer they will be. Then everybody gets off with most of the gold, to hold up a passing truck.