420SEL auto tranny question

[BENZ-LGB]

I have a 1991 420SEL with 238K miles on the ticker. The car runs fine. The engine is smooth. The tranny shifts well, on time and powerfully.

The other day, however, the tranny did something weird. After driving for about 3 miles, the tranny wouldn't shift out of first. The engine would rev up, but no shift. When the engine revved, the economy (vacuum) gauge wouldn't move past the economy (left) side. In other words, it would just stay put.

I pulled over the side of the road and the engine was idling smoothly, ruling out some sort of vacuum failure.

I put the car in PARK, turned the engine off, and then re-started it.

the car then ran fine and shifted as always--right on point.

The car, engine, and tranny have been running A-OK since then, but now I am somewhat worried about a major trans job.

I am taking my car for a regularly scheduled service on August 26. My echanic will then take a gander at the tranny.

Before I take the car to him, I'd like to hear from ayone here if they have had the same problem with the tranny. And if so, what was the solution?

Any ideas, suggestions, etc., will be greatly appreciated.