[bobcowan]

If it's a solid axle, the proper way to drain the diff is to remove the cover. That's good, because it gives you the oppurtunity to sweep out all the small filings, and inspect the parts. Lots of vehicles are that way.

To put the cover on, just use your favorite silicone sealant. I cut the heads off a couple of bolts and cut a screwdriver slot in the end. I can screw them in to act as guide pins so the cover doesn't slide around while you're getting the other bolts in place.

If you have an IRS pumpkin, then a drain hole is a welcome addition. In many apps (like my FFR), the only way to remove the cover is to remove the diff. Kind of a pain, and very messy. I drilled a hole in bottom, tapped it for a 1/4" NPT, and installed an inexpensive brass plug.

The best friction modifier is from Ford. All the diff experts I've talked to over the years recommend that for every clutch type diff they rebuild.