As soon as I thought the new modulator and Bowden Cable adjustments had given my tranny a new lease on life, I'm back to square one

THE FACTS:
Over Thanksgiving weekend I put about 150 miles on my 420 getting to our destination. Shifted into reverse and backed down a long driveway. Upon returning to Forward, the whine characteristic of reverse continued (only not so pronounced.) Whine is persistent, speed sensitive, and present in all gears and in neutral. No problem with shifting though... Transmission works fine except for the annoying whine.

When I returned home, I listened carefully, and the whining is definitely coming from inside the bell housing. I R&R'ed the fluid, filter, and gasket. I do this regularly (every 25 thousand miles or so) Absolutely no sign of metal shavings or other impurities in either the pan or filter.

QUESTION:
I don't feel competant to rebuild a transmission on my own, and given the different possible diagnoses: tranny pump, planetary gear, bearings, seals, pistons, et al. the bottom line question for me is this: With 245,000 miles on the original tranny, am I better off having a qualified tech rebuild her or should I simply have the tech swap in a replacement? (Seems to me the net cost is not all that different...)

Also, if replacing the entire tranny (and torque converter?) is the concensus here, can I rely on German Star rebuilts? Other suggestions for quality rebuilts at a fair price?

THANKS!!!

__________________
Eric

1991 560SEL-Euro (214,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)