Yep, it’s fallen out again. So Loctite didn’t work, epoxy didn’t work. I suspect the epoxy may not have got a good bond in the splined cavity, but have no way to prove that. Unfortunately, a replacement unit (because it’s the whole unit, wiring etc) is a few hundred Euro. Ouch. Perhaps I’ll see about getting up in the crawl space, or asking Paraig if he can do it, disconnect the existing unit, and do some work with a metal drill bit, thread tap, and a spare short bolt..
If that fails, I see someone on eBay is offering a third-party unit for about half the cost of a Raymarine original. Could be worth trying.