525 tds 1994 tranny sliping

[SAny]

i do have a sliping tranny in my bmw,my car is perfect almost everything looks new but this tranny is killing me,how can i replace fluids, i was looking underneath and didn't see how, i was told that only the dealer can do this job is that true ,and if now can someone out there explain me how to change oil and filter in this tranny thank you.