I just remembered I never updated this thread.

I pulled the old GPs out, no problems. Hooked each of them to an Ohm meter after pulling them out. Still reading open circuit on every one of them.

I put in a new set and she fires right up on the first rev again.

I think that a couple were out for a while, but the engine starts so well, that it made no noticeable difference. Then when a third one went a little over a month ago, it started running a little rough right after start up - my first indication something was wrong. Then the last couple went out and I got to the point of a no-start.

It doesn't seem all that unusual to me for all 5 to burn out within a period of a month or so. I mean, they were all installed brand new at the same time so there's a good chance they all came from the same production run, and they've all seen the exact same use and number of glow cycles...