Dang, just buy a new benz - problem solved...
i cannot find a oil cap for my benz.

no. the driver has photos of me he said he will sell to the tabloids if he loses his job. got to keep the car, the driver and somehow get hold of those photos.

my wife will leave me. i told her i was in geneva on a banking engagement and the tabloids show me with a young juene fille at the baccarat table in monte carlo.
i need that oil cap.

In that case, don't worry about the oil cap, just stuff an old rag into the gas tank nozzle. What could possibly go wrong?

right now i have a rubber cap stuck in the hold where the oil goes in.
there is always the possibility of engine fire.
luckily, the driver is willing to throw himself on the engine should it enflame. he is loyal even if if a blackmailer.

i've got an oil cap for a benz. looking for matching benz...
I think you might have the better bargaining position. You might have to pay up a bit for the benz, but you should be able to get the driver for free.
life can be very difficult for the rich.