Maybe a good idea to move on. A broken sunroof mechanism on the W126 sunroof is diabolically difficult to fix (the pop up feature was the weak link on them, and a little weak and prone to fail) but to get them back on to the rails is strictly a Mercedes dealer job and could hit $800 with no trouble at all.

A Mercedes dealer friend in the tech dept. of a dealer in Oklahoma City mailed me the list for the 30,000 mile service on the W126, and included in the jobs was "lubricate and lightly grease the sunroof tracks/rails"
This requires a special Mercedes Benz grease, (Incidentally, sold only in huge $10.00 tubs, and not really intended for sale to the general public, but rather to the Mercedes service departments only) and how many times you think this was done as part of the 30,000 mile service? I owned my car 10 years and never learned about it till I received this instruction.

A new transmission, if needed could be $1200 or more with no trouble at all, so if that's the trouble, it could be $2000 from the git go.

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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)