I put car in to get tyres balanced rotated today and was informed I had a major oil leak... Went home and degreased engine as right side of engine was covered in oil. ran and couldnt find anything so then took intercooler off and there was oil coming from top of engine area I was relieved as I thought it could have been a head gasket. Cleaned it down again and have found the oil coming from number 2 injector working from front of car it is trickling out and pooling on manifold. I have done a bit of reading and am a bit unsure if I should replace all 4 now or just the one and also is there anything else I shoukld replace at the same time. My car is a 2003 direct inject zd30 diesel. also is there any precautions in replacing the cups or do they just come out. do they need to be glued in or are they just placed in the hole?