It sounds like you could use a copy of Pete Snidal's superb
Bullet Service Manual found at:
http://www.enfield.20m.com/bullet1.htm. It's not only a service guide for fettling and repair, but offers lots of sensible user tips throughout for best practices on operation. It reads kind of like you're just hanging out with a knowledgeable buddy who really knows the breed.
Just to quickly clarify, the old AVL and similar predecessor "Iron Cylinder Engine" models, also called by some "pre-units", because they were "pre Unit Construction", have separate engine, primary drive (left-hand side, wherein the clutch and alternator dwell) and gear box, each using different lubricants.
The gearbox wants gear oil, preferably a straight GL-4 rated one of about SAE 90 weight. Some of the commoner GL-5 or "GL-2 through GL-5" formulations may contain added sulphur anti-impact additives which can really harm older gearboxes with copper or brass bits. If you see "GL-5" anywhere on the bottle, it's best avoided. The straight GL-4 may not be found in the automotive aisles, but you'll almost always find it in the boating section, since many outboards and outdrives also specify GL-4. Keep an eye out for "Quicksilver", Mercury's house brand. Your Enfield will like that. The gearbox drain plug is fairly obvious. Once drained, one of the lower screws near bottom left--the second or third one up(?) is your fluid level indicator screw on those 5-speed boxes. Having removed the inspection cover and level screw, you just put gear oil in through the inspection hole until it commences dribbling out the level hole. Button it all back up, and you're done...almost. The old gear oil you drained? Unless it looks like melted licorice or hippo snot, go ahead strain that with a coffee filter or even a paper towel into some clean container. Allow it to settle a week or so, and then gently pour off maybe the top ⅔ or ¾s of it into another clean wide-mouthed container with a lid, preferably a clear one, toss in a little 1 or 2 inch paint brush, and there's your chain lube. A little slop of that along the easy-to-reach bottom portion of your drive chain just forward of the brake drum after each ride, with an old cookie sheet or something to catch any drippage, and it'll both carry off any road grit, and lube your links and sprocket teeth, far extending their service lives. Just doing that bottom section means you'll be giving the whole chain a complete lube every 3 or 4 rides on average, and takes only seconds. I'm at about 18,000 miles on what I believe is the original chain, with about half the "snail adjuster" left to go.
The Primary Chaincase should take either 10W-40 or, better yet, Type F (Ford) Automatic Transmission Fluid. If you have an Electric Start, instead of the 420ml or so determined by the fluid level screw (near the bottom of the outer case, a bit forward), you might do well to put about 800ml or about ¾ of a quart to better bathe the finicky starter sprag stuff. Though frankly, you might consider NOT EVER using that electric leg as they are SO prone to failure. Oh, and that Type F ATF also makes for a perfectly fine fork oil.
The engine will like most any 15W-50, though some owners use other weights, and some diesel formulations are also popular with owners for their increased detergent and zinc (anti-wear) properties. At the risk of opening up yet another dreaded "Oil Thread", a big jug of Mobil1 15W-50 for 20-something bucks will do you just fine. Filters can be had from our Forum hosts. I personally add an ounce or two of something called Lucas TB-Zinc additive (special-ordered for pickup at Wal-Mart) to my oil, but that's entirely optional. Then again, I haven't needed to adjust my tappets in over 10,000 miles. So there's that.
All of these lubricants should be readily available on the shelves of your local Wallyworld. While you're there, you might grab a quart of Marvel Mystery Oil. An ounce or two in each tankful of fuel will keep things "happy" and help gently ease out those cobwebs if the bike's sat for a bit, especially with ethanol fuel.