last year i picked up a 83 firebird s/e as a project car the only major thng wrong was that it leaks tranny fluid while shiffting was told by owner that it was the rear main engine seal any ideas?

 

Firat, determine if it is red ATF or engine oil. And if a particular place is wet under the car.

 

As jmd stated, determine what fluid is leaking. Then, if it is ATF, and in the middle of the car where the trans bolts up to the engine, it is probably a converter seal leak. Now, those don't usually leak unless the bushing for the torque converter is worn excessivly. Look very carefully, as I have seen many that had a leak near the center of the car be from a rusted out cooling line on the passenger side of the trans.
BTW, trans removal is nessisary to replace the seal and bushing, so you could also do the rear main engine seal while the trans is out, just remove the flexplate and replace the seal.