There are numerous places a TH350 could leak. Even if you replaced the seal, there's a chance the pump bushing could have walked forward, which will cause a leak. Did you put silicone around the pump seal when you installed it? The pump has an o-ring that seals it to the case that have been known to leak. And...Don't overlook the converter hub. I've seen many of these crack at the welds. Most of the time, where the hub is welded on. The other possiblity are the pump bolts. Does it leak more while running or with the engine off?