I'm also not ruling out that I might just be an idiot.
I used copper RTV and silicone o-rings, but I also used a set of FMF springs, I didn't realize they were absolute garbage. I should have known, because I had an FMF spring break on me about ten years ago, but I thought it was a fluke. This time around, I used FMF springs almost exclusively (I think I had 1 oem spring on there), and they all broke, so that probably let the pipe move around a bit too much, causing my leaks.
The pipe never actually came off, so I just replace the springs with new OEM, but I didn't pull it off and re-assemble with new RTV. Now it's leaking all over the place.
I figured I'd ask before I pulled it off again. I'm thinking the REAL answer is less about RTV, and more about "Don't be a stupid, lazy piece of crap. Pull the pipe and do it correctly."