i have an oil leak somewhere on my 4 speed and im not shure what it is. what is the main causes of an oil leak on these trannys?

 

It depends on where the oil is coming from, have you looked at the trans yet?
If in the back, then the tailshaft seal. If in the front, then the input shaft seal. If on the driver's side, then most likely the speedometer gear housing seal/o-ring.