Going to pull the engine & trans. Noise in the trans, and the rear main is leaking. Trans noise is rotational and loudest right in the middle, will cease at low rpm with the clutch in, more obvious in neutral, 1st and 2nd, and less in 3rd. Lube drain yielded nothing, even after pushing a magnet up inside to collect anything. Prior owner probably changed it.

Any suggestions for hard part sources? I see Buick Farm has a scant few, nothing at Bob's or CARs. There's a '46 being parted out on eBay, not sure what to offer for the trans. Might be best to wait until it's out and apart on the bench, but I can't help trying to think ahead.

Wonderful forum, grateful for the help. Would love to be able to get a few more weeks of driving in before the Wisconsin winter sets in. Thanks!

Dear Chris:
From your description of the noises, I think you will probably find bearing problems in the countershaft bearings. The countergear doesn't turn with the clutch in and isn't under power in 3rd gear. Only in 1st, 2nd, and reverse is it loaded up.
Regards, Dave Corbin

Dear Chris:
Here's some specific info:

Bearing: part number 1394873 with 52 rollers (Group 4.422)
Thrust washer: 1298451 (Group 4.423)
Countershaft: 1298459 (Group 4.428)(15/16 dia. X 9 23/64 long)

These 3 items were used from 1937 thru 1948 in all big series Buicks.

Countergear: 1319382 (Group 4.421) 1941 thru 1948 all big series Buicks.

I hope all of this helps.
Regards, Dave Corbin

Thanks Dave, a huge help. We won't be pulling the engine/trans until later this month, and will see what we find.