So another week, another update. Ordered a bunch of parts from Great Plains Electronics and they came in yesterday - so I immediately replaced the caps on the SB-100. Outcome was good - not 100%, but good. The very loud buzz noise that overpowered everything has been replaced by some white noise/staticy background noise but the game sounds are much louder, clearer and very crisp. Overall, a 90% improvement that puts it into "playable" sound from my perspective even if not perfect.
I also tried pulling up the playfield to work on it - there's definitely no prop stick unfortunately. There looks like a metal rail on the right side of the internal body that used to have something there to prop, but...nothing's there now.
I soldiered on and tested the one kicker/solenoid that isn't firing - but I'm not certain how to fix. The switch looks like one of these: http://www.marcospecialties.com/pinball-parts/SW-1A-130 and the plastic piece at the end (where the ball hits) is worn down a bit. However, the switch doesn't seem to be 'staying on' - and it seems each kicker hole scores 3 times (i.e., 3 noises) then 'activates'. If I hold the switch down manually, it seems to take a bit of time to kick on and is intermittent. I'm going to check the underside a bit better once I can get the entire playfield out, but from what I could see the switch is definitely closed when a ball is in the hole - so something else is broken/shorting in that path...which doesn't sound fun to figure out. Any ideas on trouble shooting would be appreciated.