"I was careful to use silicone under every fastener when re-installing, as I
suspect that may have been my leak source before (I was never able to pin it
down)."

Me too. I'm using a Trevor Reid iteration of moon-viewer (OEM one was
sun-cracked badly) and I've been in several heavy rain situations and have
had no leaking at all. Silicone sealer on all the hardware
holes/applications is a very good idea.

Bob