Hi guys thought i would fill you in on some facts about common rail injector repair.I have a friend who is a bosch diesel center as well as a main agent for DENSO,ZEXEL,DELPHI,and STANADYNE he has been repairing bosch common rail injectors for over 5 years and gave me an insight to what is involved. Common rail injectors are very difficult to repair PROPERLY and should only be attempted by authorized repairers and not non genuine guys like darwin diesels and David Braebrook (db diesels )as he has tested them on his bosch 815 test bench and found them to fail on nearly all tests not just leakage as they have not been repaired the correct way and would have caused engine damage after a period of time.High back leakage can be caused not just by the seal but usually due to the pilot valve seat being worn where the ball sits.Once you have stripped the injector the cap nut must be repaced along with the ball, seal, pins(2) and straining screw as on assembley these are torqued then set to a manufacture angle torque this is the define setting value and all injectors are different failure to get this correct will cause pre injection to happen along with light load fuel figures to be out.He also assembles them in a micro cabbinet as cleaniness is the most important factor. Once assembled he then tests them on his 815 bench where they are tested up to 1700 bar and once fully tested a new IMA code is written by the bench for coding purposes.As he does hundreds of these a month i get a very competitive price usually around £90 each so why get yourselves into a mess trying to fix these on the cheap .Hope this answers any questions you have on trying to have a go yourselves.