I screwed around with this very issue last year at around 153K.
First, I'd check under the car for any sign of leaks. Your fluid level may be down. In my case, I didnt have a leak.
Changed the fluid and filter. The filter was the old style which had collapsed on itself.
Get a Filtran filter from BMW dealer; fluid was Pennzoil Multivehicle ATF.
Cheap, and it works.
Did the "slop fluid in the face" fillup. Look in the archives for the fluid/filter R&R.
It was fine for about three months. Changed the fluid again.
It improved for another 3 months then the shifting went dangerously bad.
I finally replaced with a rebuilt 5HP30 last month.
I checked my records and the valve body had been replaced by BMW/ZF at 85K. So i figured the trans was just wearing out.
Ramon
1994 540iA Nikasil EAT Chip
Tampa Bay, Florida USA