Is bad injector pump on 300TDT really "nothing to worry about"???

I recently purchased an '82 300TDT w/ 268k. It didn't cost much, but it looks like it's about to. I missed all this in a short test drive, but since I bought it, I noticed that after I drive it about 15 minutes, it will shake badly at stops. I told this to my mechanic, whom I feel some loyalty to, and he said it was a common problem, nothing to worry about. He said it was a bad cylinder in the fuel injector pump which starts causing trouble after the car warms up, and that at $1000 part+labor, it wasn't worth fixing on my car. So I didn't worry at first, but now the shaking has begun starting sooner, and it also shakes when I brake to stop or when the car naturally decelerates down to a stop. (brakes&rotors brand new so it's not that, but that's about what it feels like)It's gone from bad to worse in 2 weeks. My questions are: Should I have other things checked out? Am I right in thinking this problem is not going to go away but will get worse? Also, I have always wanted a wagon, it would be worth it to me to spend the money IF that's really the problem...am I crazy? Thanks in advance for all advice!!!