You need new ones, if they fail its the injector housing that fails - meaning a service/rep kit will do no good (normally). Tried to rebuild a couple of failed ones at a Bosch specialist with all special tools and test equippment but to no luck.
yes bosch said same thing here they have tried rebuilding them and high pressure test passes but they leakback excessively due to worn housing that is virtually undetectable till you test it out after rebuild, an expensive gamble im not willing to take !