Audio Systems: 1987 Becker grand prix 754 cassette player, becker grand prix, sirius radio

Question
Hi, i recently purchased a 1987 Mercedes 300 SDL with a becker grand prix model 754 stereo AM, FM cassette radio. everything seems to work but the cassette player accepts the tape, then it switches tracks and purges the tape....i'm wondering if i am doing something wrong or if you can advise me what to do. also, i'm expecting a sirius radio kit on Monday and want to install it, any advice would be greatly appreciated.
 the car has had a second antenna installed but it seems to be working fine with the radio......the old appears to be broken.  

Answer
this radio tape runs on belts and one of the them is old and needs to be repalce also it will be a good idea to clean the cassette with contact cleaner wait about a couple of hours and put grease back on the unit  and replace all the belts  
it will work like new
good luck