The resistor was right where you said...under the brake booster.... and hard to see and harder to replace, as you said. On visual inspection it was obviously dead. The only way I could get it out was to take a long shafted screw driver and break the leads off. That allowed me to hook the two leads and pull them up to where I could just barely get connectors installed. Then I jumper wired the two leads, so the fan runs on high speed.
The car has never run better in this 105 degree Las Vegas heat. When I get the new resistor I'll relocate it to a more accessible place. Thank you so much for lending your expertise!
P.S. - Dave, I don't know if you want to try this "last resort" removal and replace methodology, but I honestly couldn't see any other practical way to do it.
Don's 500SEL Euro