Well, the solution just occurred to me a few days ago.
Firstly, I still occasionally get the flashing rear defrost light, but the charging system was perfect otherwise.
Well my blinkers are irratic (hazards too), my intermittent wiper work 5% of the time, and my rear defrost gets low voltage....
It's all in that one combo relay!
Part No. 000-821-08-63 is selling for only $41.77 in Fastlane! I'll be ordering that now.