Rough Idle, Nailing Diagnostic Questions

[shertex]

Sixto and GSXR have given me some good advice via email....thought I'd see if others have thoughts....and perhaps this thread could help others with similar symptoms.

Newly acquired 1987 300TD has the following symptoms:

1. Rough idle, with rhythmic puff at tailpipe
2. Nailing under moderate load
3. Fuel leaking at top of IP
4. 4 of the 6 splined collars for delivery valves are missing

In another thread, Sixto indicated that the nailing and the rough idle could be explained solely in terms of the leak. BUT, I'm also fearing more costly possibilities, e.g. bad IP or injectors.

My working assumption is that, diagnostically, all I can really do at this point is replace the delivery valves seals and see what happens. Is there any other approach to take? Would be glad to hear anyone's experience or input.