'89 240DL, 160K miles, well maintained but no records about transmission servicing.

The history of it is that my wife was noticing lately that the car wouldn't shift into certain gears. The problem was intermittent, and came on pretty recently. No funny sounds or other symptoms until now. I first suspected the OD relay but swapping that didn't help, plus then I noticed the problem happened going into all gears, so obviously it's not an overdrive issue.

Another possibly related thing is that the accelerator pedal seems to have been a little sticky. I lubricated the cable at both ends and that part seems to have gone away, but originally I was thinking that that symptom might indicate something with the kickdown cable.

Anyway, I flushed the fluid and if anything the problem got worse. So now I'm also suspecting a clogged up transmission fluid filter.

Am I on the right track here? What do you think is most likely? If I can fix this problem without draining it and dropping the pan - that's a pain in the ass and a really messy job to do in the driveway on a rainy day - I'd love to hear some more ideas.

By the way, what are the symptoms of an M46 dying?