I have a 91 3.0 lwb monty with the 5 speed. A few questions:

1. Read all I could find on correct manual tranny fluid (gl-4 vs gl-5)my original owners manual states to use the gl-4 but I cant seem to find any. I have 80-90w gl-5 that the label says meets requirements of gl-4..but all I have found to read say that the gl-5 will not work well inside the manual tranny, with the copper or brass material inside.
2. The bottom of the tranny is wet. I seem to burn a quart or two of oil in the engine every 1000 miles. Is this from the rear seal. I have NO spotting in my garage or driveway, is it the rear seal failing when under pressure (driving?).
Or is the wet from my tranny ?
3. Confirming that drain hole is actually horizontal at the bottom of my tranny (not pointing to the ground but on drivers side pointing towards the driver door) and fill hole about 3-4 inches directly above...and if anyone knows offhand, what size are the plugs.

She shifts fine, I have put 10k miles on monty last 8 months and do not know when PO changed or filled tranny fluid last. Shes my DD. Just completed brakes and installed a new rebuilt starter.

Thanks in advance for your help....