Hello, I have just bought my first Mercedes, a 1991 W126 500 SEL. (bought it for a bit of fun.) Unfortunately the car did not come with any service history so I'm going to assume that it needs a full service including timing belt etc. I also want to check the transmission fluid level. I've managed to find the transmission dipstick location but I am totally foxed by the red cap which doesn't seem to want to come off. Please advise.