On my 123 300CD I got a bicycle nylon bag that had a plastic cup holder in it. Removed the cup holder and had an upolstery shop cut out the foam in the center fold down arm rest. I installed the holder and secured it in the armrest with black RTV. The cup holder had a plastic ring around the holder about an inch wide that covered the cut vinyl.

__________________
81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.