B&K EX 4420 vs B&K EX 4420 reference

Bill I have my B&K EX4420 hooked up to the Adcom GFP 565 preamp, you know the Stereophile Class B Adcom pre. Anyway these older components sound amazing together. I have two systems I like them both equally even though one is more expensive.

I am looking at one for on this site, for sale now- do you have any idea of what I would expect for repairs to keep it running another 10 years? 

Spare right & left circuit boards would be nice to have. My former EX4420 was a nice sounding amp I enjoyed for over 20+ years. It got rather hot and parts inside degraded over time, hum. Had the boards repaired multiple times until I sold it for parts, unfortunately. ATI amplifiers bought B&K brand, and designs, seemingly no leftover parts. Called them multiple times with little luck or interest on their part. 

I once owned the B&K ST140. Purchased in 1985. Around 2010 before B&K went out of business I call then about a check up and possible refurbish. They said that it would need new output boards as the trannys were no longer available.  I truly like that amp, thought it to be one of the best amplifiers available under $1000 at that time. I was able to purchase it with a B&K Pro10 MC preamp from a dealer friend of mine for $850.  I later heard the EX442 which had greater power in his store, also great at it's price. I believe it to be the fore runner to the EX4420. 

@mendef All that said, I believe I would look for a used amplifier of more recent vintage.