1979 Chevy Silverado tranny question.

[JROC's Chevy]

Hello guys, got a question. I have a TH400 transmission bolted to a 350 engine. My truck has been in the shop due to a leaking transmission. I got a call today that the front tranny pump is causing the leak and pan needs to be replaced. I was told to replace the pump, I might as well have the tanny rebuilt. The cost of the total repair is in the neighborhood of $1500. I am not a transmission guy, so I dont know a lot about them but I have seen some online, through companies such as Jegs for $900/$1200 new/rebuilt. My question is, am I better of repairing mine or buying the new one and using the fly wheel and torque converter of the broken tranny?

Thanks, Jason