i recently replaced my clutch on my 92 explorer, and also replaced my rear main seal(it was leaking). i was talking to a couple of mechanics that told me to buy a seal from ford, because it came with some special shim that needed to be installed. after fighting the shim for 3 hrs., i gave up and installed the seal without the shim. the rear main leaks more now than before. is there some special tool that the mechanics forgot to mention to install the seal, or should i just take it in to have it professionally done?