To repair, rebuild, or toss?

I used to own one of the predecessors to that amp, a Rotel RB 980BX. Bought it used for $300 many years ago, Great amp for the money. That being said, I would never spend hundreds to rebuild it if it had died on me. 

You have received some great suggestions from other members. I don't think you need to spend $10,000 for a great amp. Unless your enamored with your preamp, I I would also check out some modern integrated amps. Amps from makers such as Hegel, Rega, Primere, Arcam all make integrated amps with over 100 WPC for under $5K. Just a thought.

I wouldn't repair or refurbish it...it was a good budget amp in it's day (I had one) but current amps from Schiit or Odyssey I think are significantly better, and can be found for $600 used but only a year or two old, and new for not much more...those are brands I've owned but there are many others in your price range...

Unfortunately, compromises in tonal balance and subtlety are sometimes encumbered as well, and the resulting tonal inaccuracies are often flaunted as a distinctive "character."   ~ Stereophile

Not worth it. 

If you want something right now and decide to go slow consider something like this inexpensive  (see link below) well reviewed 100-200 watt power amp that comes with a 5 year warranty.

It can also be returned within 15 days for a 5% fee (plus I assume return shipping).

If it hits the spot then two can be use as mono blocks if you feel the need for even more power.

The Marantz you are using as a preamp is also well reviewed (even for 2 channel), but if you don't need or use the other functions then research preamps.

https://www.schiit.com/products/vidar-2f

DeKay

I concur with jl35 and lanx0003.  Time to move onward.  Perhaps fix and flip as a option B.  Audiogon has lots of fine, lightly used amps for sale....check out their listings!  Good Luck!