Greetings, folks. I'm kind of new here, been lurking for a while, but need some help now, and appreciate any advice y'all have.

The transmission on my 84 300D (about 210,000 miles) has started slipping in 3rd gear. And by slipping, I don't mean flaring or slow shifting. When it goes into 3rd, it will pull for a few seconds, then just let go. The engine will spin, and there is no pull whatsoever. This started pretty much out of the blue, after sitting in the garage for about a week. The only indication of anything being wrong before that was that a week or two prior, the tranny had occasionally had trouble going from 3rd to 4th at highway speeds. The transmission filter and fluid have been changed about every 25,000 miles since I've owned the car.

I've searched the archives, but it's not clear to me. Is this something that could be caused by incorrect vacuum or linkage, or am I looking at a tranny rebuild? I find it hard to believe that the transmission would fail so dramatically, so quickly (but what do I know?)!