+1 for having a Mac qualified tech go through it.
My take is that these SS Mac's are bombproof ...when they're at spec. There's tons of posts on this forum of guys messing up outputs, and generally brutalizing these amps. They are tanks. There has to be 40+ guys here that are regularly gigging them. Not easy on a piece of equipment that's technically a home article.
I have 2. 2100 & a 250. The 2100 has been thoroughly serviced, and resides on my home stereo. I don't need the power, and I just want to keep it exercised. I bought it for about $200 working & spent $300 or so to have it cleaned up. The 250 will get service, but it's my daily driver.
The other angle is this...will it ever lose value? If you quit guitar tomorrow could you not preamp tap your reciever & enjoy Jerry sweetly through your stereo for 40 more years? Your grandchildren will have the funniest looks on their faces when they try to figure out WTF it is!
They are elegant masterworks of US engineering from a bygone era. Love it. Keep it up. Other than a MC40 or MC75 tube, what more beautiful thing is there for a dude? Unless you have a Ferrari, or my old '69 Mach 1, or a Ibby Musician, or a Travis Bean, or a Moriarty...but I digress.