Hello dieselfans,
I've just gotten myself into an '83 manual 240D, 250K or so, the first car I've ever owned. I read a lot of the peachparts forum before I bought it - you all sold me. I figured it would be a good car to learn on.
I'm stuck on a problem and looking for help with diagnosis and repair. There seems to be some play or worn part somewhere in the powertrain. When I'm accelerating in any gear, the car runs great, but when I let off the accelerator a bit, I get this clunk or knock somewhere. Then when I go to accelerate, I hear it again. It seems as if there's some worn element of the powertrain somewhere that doesn't interlock snugly against the subsequent element of the powertrain.
I got under the car with the transmission in first gear and noticed that the driveshaft seems to give me about 20 degrees of rotation. I've already checked the front and rear flex plates, the center bearing, the U joints, and the differential. All of them seem to have almost no play and be in good shape. The only place I've noticed anything is in the transmission. I can hear a soft tap sound when I turn the driveshaft from one extreme to the other.
Any thoughts? Does it sound like a worn part in the transmission, or is there some other part I should check? Before I start tinkering with the transmission, I'd like to have an idea of what I might be looking for and if I'll be able to handle the repair. The most complicated thing I've done to a car is replace an alternator.

Thanks for any help! You all have already helped me diagnose a worn steering gear

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Newbie DIY mechanic with an '83 manual 240D