I did as promised a few days ago and checked the brake bulbs. Before I started, gas gauge was inop and brake lights worked fine. One bulb looked a bit corroded inside; once I put it all back together it stopped working. Replaced both with new 7443s from Autozone.

I was probably around half a tank at the time. Gauge wandered a bit at first between trips but no more of the needle drop and blinking gas light. Stabilized after 2-3 days and read normally. Just added 16.5 gallons with gauge showing 1/4 tank, needle is back above F and held there for the 10 miles I've driven since then. If something changes I'll report back, but replacing the brake lights seemed to reverse whatever gremlin popped up when the battery ran down a few weeks ago.

Weird.