I had exactly the same experience on my '86 740GLE w/M-46 six years ago, when the car had 100,000 miles on it. I drained the Dexron (noting much particulate from damaged O/D clutch facings and probably bearings, too) and removed the O/D sump. I cleaned both filters (the one you'll find just inside the sump and the fine filter inside the plug that you're supposed to use a spanner wrench to remove, but I have R&R'd with a couple of closely fitting punches and a prybar crosswise between them) and refilled with ATF type F. Haven't touched it since then, except for (many) electric repairs. My wife and I have driven the car another 89,000 miles (189,000 total on the car) and the O/D clutch bearing has been noisy the entire time. (This is the bearing that is noisy when the O/D is disengaged, and quiet when the O/D is engaged.) The O/D itself has recovered pretty well. Initially, it had trouble with engagement. I think that the Dexron did a number on the engagement piston o-rings, too. I have no intention of taking apart the O/D. Unless your O/D clutch bearing is really loud, I would change the fluid, clean the filters, and not worry about it. Good luck.