I found out from the dealer that my 86 635 had a new tranny installed at 85,000mi. My car now has 110,000mi. I could not find out from the dealer if the tranny fluid had ever been changed. Should I change the tranny fluid if the fluid that is in there now it 25,ooomi. old or would I be asking for trouble(seal leaks, etc.)? if so should I use synthetic or regular? thanks in advance for the advice