My 92 300TE started doing that around 210K, after I bought it. I put in Lucas in the tranny, and it was OK for maybe six months. But finally the it would not reverse. I drove until 303K, then disposed of the car. You can extend your operating time by pulling thru parking places, and looking for places where you can park "uphill" and roll back in "N". So I drove it at least a year with no reverse.

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91 300 TE 235K
93 Cabriolet 155K sold
92 300 TE 200K boneyard