A few days ago the rearview mirror in my car parted company with the windscreen glass. Looks like it had been re-(super?)glued before.

So I read up on a number of (un)suggested glues: the double-sided sticky pads are a wobbly joke, especially for mirrors of normal size (and weight).

Superglue seems to be iffy because it might make your screen crack (apparently some thermal expansion issue regarding the crystalline nature of the hardened cyanoacrylate).

The special-purpose rearview mirror glues do not always work well (but that might also be sloppy installation). Interestingly, most of those are CA-based and none are really cheap.

The three most interesting suggestions I found were No-Nails construction glue, bog-standard silicone sealant/caulk and silicone RTV gasket maker. My last tube of (clone) no-nails had dried out last year, the sealant cartridge I'd have to clean of the usual dried out plug in the nozzle so I went for the gasket maker - which is Black, an additional benefit as #000000 rules the universe.

I sanded down the metal back of the mirror mounting block and scraped off the glue crusts on the windscreen, wiped everything with alcohol. On the Sooby the mounting spot is painted(?) black, and most of that paint even survived the scraping (but did I mention that the gasket maker is a Matching Black?). Dabbed some gasket goo on and pressed the mounting block into place, waited 6 hrs, tried it out: nope, too wobbly and not sufficiently cured yet, so with the mirror weight everything fell off. I simply pushed the block back on, waited another 18 hrs: perfect. Good, fast, cheap: pick all three :-)