Rear main seal

[JAM1777]

Hi everyone. I have a 69 C10 longbed that i bought with a rebuilt 350 smallblock. I noticed alot of leaks so i took it to a shop and got an estimate and they said it was the rear main, the transmission gasket, valve cover gaskets, speedometer connection on the tranny and a seal on the side of the tranny, and it would be $1500. So i replaced the valve cover gaskets and i had a friend do everything else for $600. I got the truck back and it was still leaking. My friend said it was the oil pan cause it was old and warped. So i ordered a new oil pan and fel pro gasket and put it on myself in the driveway which was very challenging and topped off oil on dipstick and looked under truck.......STILL LEAKING!! So i took it to a local shop yesterday and asked the guy to find out what was going on. I called him a few minutes ago and he said its definately coming from the REAR MAIN SEAL. I said i just had it changed and he said if i just had it changed then there may be something wrong with the motor. Im really frustrated and dont really know where to go from here. So i have some questions..........if its coming from the rear main seal and i just had it changed, what else could it be?? Did my friend maybe put it on wrong?? Is there something else behind the rear main seal that can go bad and cause the rear main to leak even though its new? Im kinda at my witts end.....any help would be very appreciated.