So I tried a thing.
I've had the vacuum pump off before, and it isn't fun. So I looked at this thing for a bit, and decided I'd try to fix the leak without removing it. If you have a LHD vehicle, and if you remove the air filter, you might be able to pull it off. But some vehicles might have other things in the way.
Using an angle drill, a chisel, and a nail to punch left overs through, I was able to get each of the rivets out. I pulled the top off and found that the pump "looks" fine, and that someone had already been in there. The o-ring was already covered with black RVT type stuff. The fact that these were rivets put in by a DIY'er, and more than one of them was not really very tight, gave me hope. Maybe they never pulled the lid as tight as they could have.
I did my best to clean up the o-ring, but all along I'm thinking I'm going to rely more on the sealant than the rubber. I then realized that my Right Stuff was solid in the tube....... so I had to resort to some standard Permatex Black Silicone. Which is not bad stuff, it's just not Right Stuff. I smeared a bit on both surfaces, and made sure that the reused o-ring was well in it in its groove, then I used a set of #8, 3/4 inch screws and lock nuts to tighten down on the lid. I don't know how tight it should be, so I simply did my best to get them even, and to guess at how much would be enough. The nice thing is, if it does leak, I could at lest try to tighten it more now. And if that doesn't work, I'll go get some Right Stuff and try again.
I let it sit for 24 hours, then started the car and let it run, revved it a bit, then shut it off and checked for a leak. It is certainly better than it was. Nothing is coming out yet. But time will tell. I'll actually drive it tomorrow, and check a few more times before I'm sure it worked.
I should have gotten a different type of nut/bolt combo. Maybe an M5 or M6 by 20mm with nylock nuts and Allen heads would have been better. However, I was able to use a screw driver on each of the bolts from the outside, while holding the nut on the back side with a small spanner. A larger nut might not fit the space, but if you had Allen head bolts, you could put them in from the back, and bolt from the front.
Anyway, it may be that I fixed the leak. But I did prove that it can be done without that extra step of removing the replacing the pump itself, which should save some time and frustration.
If it does not leak, I should now be able to tell where my other leaks are coming from, and get a better sense of how bad they are. I'm sure this leak was the main culprit, and was contributing to the other drips in some way.