As i was replacing my rear main seal, i popped out the old and read in the book "Measure with a feeler gauge the old seal and make sure the new is the same". I went ahead and hammered in the new one with a board until it was flush and figured it'd be okay, i put the engine together, get it back in, start it, i pour oil out from the main seal. It doesn't say in the book the specific spacing for the seal, can anyone tell me?