is the main transmission seal seated just around where the input shaft comes from the back of the tranny to the front? The reason I ask is because my clutch was slipping badly, so I take her all apart to find out that the clutch meat looks just as big as my new replacement, but I seem to have oil on the transmission end of the flywheel but not the rear end indicating theres not a problem with my engine seal. Am I correct?

 

Sounds like a leaky input shaft seal. You will need to disassemble the tranny to replace it. It is directly behind the ISB.

 

could i just use a heavier gear fluid instead of 10w-30 like gear oil or 10w40 or even straight 40 to stop the leak