Rear Main seal

Surre it can. If it still has the rope seal in it, there is a tool kit KD Tools sells, with a "chinese finger cuff" type dohicky, and a few picks and stuff to get the upper 1/2 out. But, if you just swapped the pump, and the rear main didnt leak before, I'd lean more towards perhaps a pan gasket or end seal leaking. It's difficult to get all the oil off the mating surfaces, and if you dont clean it very well, no gasket or RTV will keep it sealed for long.