Steev et al,
I showed my wife the postings on this topic and web pages as it is her bike. Rather than buying a used one, she'd rather have one with warranty.
So we ordered one new for ~$40, which I have just installed. It is much brighter than the one she had - even if all LEDs had worked, especially when she hits the brake. And the blinkers are quite visible, too. So now we have a spare clear taillight lens and extra ballast resistors as I reused the old ones, after I made sure that everything was now tight and prevented from vibrating around as much as I could stop it.
Thanks for all your insights.
Guess we can close this topic now...