Tried the freezer spray today on the power supply board caps, ipms, Ysus fets, mainboard ic, and control board ic the best I could. Was not able to find anything. Thought I would try a hairdryer in the next day or two, to see if the opposite approach helps out over the 5+ minute startup problem.
May try to check the control board voltage regulators when I get it flat on its back again, and recheck the Ysus fets again too.
Not having the necessary tools handy is a pain, so board replacement approach may be the way things have to go. Will update as things move along.
P.S. The Vs (supply) is 187.6V against a 186V sticker value, surely that can't make a huge difference?