Early Slant 6 Rebuild

my68barracuda said
To get to the rear main seal on a slant you will need to drop the oil pan.
To get the oil pan out if you are working on an A body you will need to at least remove the motor mounts and tilt and lift the engine up.
After doing all of that, trying to get the top half of the seal changed, trying to get the oil pan re sealed, while working on an engine in chassis,,, is a lot of effort without a great chance of success.
I would pull the engine to change the rear seal, or wait and change it when the engine is rebuilt.

It would be worth the time to do a quick investigation as to why it is leaking oil,,,
Did some of the oil pan bolts get loose?
Is there excess / non vented pressure in the crankcase from a plugged PCV system or road draft tube?
Has piston ring blow by got so bad that the crankcase vent system can’t keep up?
Is there thrust bearing worn and the crank end play is out of specification?

The oil pan is sealed tight. The leak is coming right at the bottom of where the engine and transmission meet.

As to why it’s started leaking in the past 2 weeks, no clue. I’ve been driving with this motor for about a year now. I had a ton of maintenance done when i first bought the car, which included new timing, new oil pump, new valve cover gasket and oil pan gasket, etc. And have had one tune up done and done another myself. But it’s not a very fun leak, I lost a quart of oil in ~2 weeks. Previously i went almost 2 months before i was noticeably down (not even a quart, maybe half a quart), And by then i was due for An oil change. But now it’s leaking like a sieve.