As a follow-up, I thought I'd post and let you know that I was able to
swap the top (broil) and bottom (bake) glow-bars, and this did resolve
oven temperature problem. Thanks everyone for their input.

I tested the broil function briefly (for about 15 minutes) and did not
see any problems there either. I was kind of hoping that broiling
would now not be working properly, as that would undisputedly finger
the faulty part. Since this problem was intermittent, It could just
be that I didn't test long enough to see the problem. Or possibly
there was a flakey connection that was fixed during the swap. Either
way, I now have a functioning oven. I almost never use the broil
feature anyway, usually opting for the gas grill outside instead - so
it may be a long time before I notice if the broiler is now
malfunctioning.

-J