A Chandler dealer's SA was reviewing my 98 ML320s service history and when he noted 123,000 miles he suggested I start saving up for a new transmission as he felt 125,000 was about the average. $5000 plus for a dealer replacement.

I immediately changed the ATF to Mobil 1 (not factory fluid) and am now at 131,000 miles. My 79 300SD, which slipped for years, is now shifting as good as new and has 261,000 miles with only a new accumulator. Also on Mobil 1 ATF.

It should be noted that when a dealer declares a transmission dead, it is the only expedient thing they can do to minimize come-backs. The first failure could be as simple as a gear selection solenoid failure, easily replaced, but probably the first in a chain of failures that the dealer would wish to avoid.

Just my opinion, YMMV.

Jim