When I first moved to Oxford, there were a lot of colleagues who had worked there for many years, and had stories to tell.
For a long time, many workers travelled on foot or by bicycle. Cycles were parked inside the otherwise secure area, whereas cars were outside.
When a shift ended, there would be a mass exodus. Parts being carried out would be in the middle of the crowd, often large items such as wheels, or even complete seats. Once a whole engine, suspended between two bicycles, and the gearbox a few days later.
There were many Cowley built vehicles around Oxford, low spec models bearing alloy wheels, plush interiors, etc.
Not surprising when security focussed on my Fiat because it was unusual.
I was in an office building, 6 storeys tall. We could look down on the trucks leaving the parts warehouse. One day a truck trundled by with a complete exhaust system on top of it. Head of security had an office on the top floor, that side of the building, and he saw it too, so it got stopped at the gate.
Small items could just be put in a jiffy and posted out. Not sure if they ever woke up to that one. When I was dealing with carburettor parts, I used to post large jiffy bags daily, never checked, just trust. Whilst I never sent anything that shouldn't have gone, it did occur to me that I could have done. Surely this must have occurred to others over the years.