Tranny leak test?

I replaced all the seals on my 65k mile AWD tranny when I had it out/open for a bell housing brace. In what was in retrospect a poor decision, I used an aftermarket input bearing/seal to save money - OEM seals everywhere else. I would have been better off reusing the original bearing seal (which wasn't leaking).

Tranny ending up leaking badly within 100 miles and ruined the new clutch. Tranny oil (not engine oil) was everywhere inside the bell housing so it was hard to pinpoint the source but it appears to be traveling down the input shaft until it gets thrown. Output shaft seal does not appear to be source of leak.

I've now replaced the input bearing/seal with a very expensive / rare OEM bearing/seal and replaced the output shaft seal and drivers side half shaft seal again with OEM seals while I was there. Tranny is now back together and I'm waiting for new clutch to arrive.

There was no visible damage/problems with the aftermarket bearing/seal, o-ring, or the input shaft.

Question - is there a good way to test the input / output shaft seals for leaks before reinstalling? I could simply fill it will oil which would put the oil level below the front output shaft seals and watch it for a few days, but with nothing spinning is that sufficient?

Filling it and waiting may be sufficient, if you are extra worried you could make a piece to chuck in your drill from an old clutch hub and spin the trans for a few minutes in neutral. Just make sure it doesn't sling oil out of the axle holes if you put it in gear.

I've also thought about bench testing transmissions by taking an old t-case spool and welding it to a bolt to chuck in a drill. You could spin the output shaft and go through the gears, checking for grinding. You would likely need a corded 1/2" drill to have enough torque or some type of gear reduction one. I've seen a guy on youtube test a miata transmission using a drill press to spin a driveshaft going into the trans.

Thanks. I think the input shaft sits above the static fluid level in the tranny so I was thinking of rotating the box until the input shaft was below the fluid level while keeping the axle holes above it