I’m still suspicious that the regional guy is being lied to by the original mechanic. It’s a pretty startling coincidence to have a rear main seal go right after an oil change. It can happen, but… Coincidence. If I notice an oil leak immediately after an oil change I suspect they either spilled oil, double-gasketed the filter, or messed up the drainplug (crossthread, re-used the crush washer, forgot to torque it down, something like that).
I’m also suspicious because the mechanic should have known that aerosol glue or gasket sealer or hairspray or whatever he “sprayed” on the rear main seal was not going to fix the thing. That tells me he either didn’t know that, in which case I question his ability to diagnose a rear main seal leak in the first place, or he did know that and did it anyway in which case I question his sanity.
I’m thirdly suspicious because you say the car didn’t start dying until after the leak was already dropping giant oil puddles on the ground. That would mean the mechanic took the transmission off looking for the cause of a problem that hadn’t happened yet, and that makes no sense. There’s still something fishy in this story chain, and that would cause me to bring the car to a real mechanic for an inspection after their second guy gets done with it, just to make sure they didn’t hork something else up that might wreck your engine.
And like the others have said, never take your car to a chain like that again, though I suspect you’ve already internalized that lesson.