From my many years of experience with Diesels, mostly of ships, and seeing as how you already have the pump off, I would take it to an injector shop and get it gone through or exchanged for a rebuilt. The insides of these pumps is not for the feint of heart. Plus it is probably 25+ years old and needs an overhaul and re-calibration anyway. It won't be cheap but you will probably never have to worry about it again for the life of the car.