Transmission leaking....sometimes

[Jeepwm69]

Got the transmission rebuilt on dad's 95 GMC a few months ago. Thus far everything has worked great. Then he calls me and says there is a puddle of what appears to be ATF on the ground under the truck. I go by, and sure enough, it has a leak. I crawl up under the truck to try to ascertain where the leak is, and can't tell. Dripping a little off the front of the heat shield on the right side of the transmission, and the bottom of the bellhousing is wet as well.

I check the fluid level and it's perfect on the dipstick (didn't have to add any) drive it 30 miles back to the shop that rebuilt the transmission and drop it off. When I get there I look under the truck and nothing is leaking/ dripping.

They put it on the rack and called and said they couldn't find any leak. Removed the dust cover, said RMS on engine is fine, and they couldn't see where the transmission would have been leaking anywhere. Oil level is a little low and there are signs of seepage from top of engine, either valve covers or perhaps the oil sending unit, and suggested it might have been oil.

I drive it back home, 30 miles, and park it, and again, nothing is leaking or dripping. Tell dad what the shop says and he points to a clear plastic container that we put under the truck when he first noticed the puddle, and there is bright red ATV in it. Not much. Maybe a tablespoon at most, but obviously ATF.

But since it's not leaking now, not sure what we or the shop can do with it until the leak presents itself again.

Where all should I be looking at this thing, and has anyone ever had an intermittent leak from one of these transmissions? Doesn't make sense, but it was obviously leaking and then stopped leaking with no action on our part.