re to the ply
it appeard to be coming from the inspection plate, but i knew the vally drained right off the back of the block. so i wasnt to worried about it being a rear main seal. check the valley. especially by the injection pump. before the o-rings went completely i found a lil oil in there. but had no idea where it was coming from. so i checked all the orings and noticed alot of oil around the pump. procastinated to long on fixing it then one day, great falls broke lose and i was leaking a crap load of oil. with truck running and a flash light, isolated to the 3 hpop seals. only two were bad but replaced all. if you have any questions or want pic my aim is dslcntry. i took pix of the whole deal.