Woops, missed the last post - sorry. Sounds like you have an air leak in the supply side somewhere, causing the starting problem on a hill, or when the tank isn't full.
The injector leak is either bad return hoses (the little braided ones - replace them if they're old), or the injector body is leaking. There is no seal inside, there are just machined surfaces that are supposed to be perfectly flat, and seal together. You can try and tighten the top half to the bottom, but it's easier done in a bench vise. If the injector is removed, the heat shield must be replaced.
If you're a recent owner of the 1987 300D, you might want to read this arrticle:
http://www.w124performance.com/docs/mb/articles/124.1x3_buying_tips.txt
