trans leaking again after rebuild

Same converter? I think I mentioned it in your other post, I had a faulty converter that pushed fluid out the vent. Did they check yours out or test it for you? There's only 2 places to leak from, front seal or vent hole. With a slow drip I'd guess overzealous install of converter on the input shaft or lack of lube, nicked the seal maybe?
If all the parts are there in front of them and the trans is clean they could assemble it in a couple hours no prob.