Transmission output sleeve bearing blows seal

1993 Nissan Maxima sohc v6 A/T with 120k miles and 30k since transmission rebuild by a shady mechanic (probably just swapped with a different trans)

I see a lot of problems where the transmission leaks, and I dropped mine out to see that it was gushing from the main seal. A sleeve bearing that seems to stabilize the drive shaft in the bell housing seemed to have forced the seal out, but I have no idea why -- if it was a sudden thing or over a long period of time. The sleeve should have been way down inside, but came completely out to meet the torque converter. I pushed it back in and peened it, hoping it will stay, but I don't know for how long. Any ideas why this happened and how to fix it if the seal gets pushed out again? I'm having trouble finding information about the transmission (ie. Dealer repairs/recalls) or about that sleeve bearing -- is it even necessary, can it be replaced with a better one that fits snug? I'm hoping that the problem doesn't have anything to do with the oil pump because it seems to have good pressure and is drivable for now (if it was bad I would think it would blow almost immediately or not even drive) Thanks so much for taking the time to help guys, this is a really nice gesture!