Blue Circle Gear?

"There is an authorized service shop for Blue Circle."

That would be-

https://www.dtsaudioelectronics.com/Authorized-Service.html

I don’t have experience with their preamps but did own a BC-204 amp that had issues. I would cringe every time I turned the amp on because I sometimes I would hear a loud pop noise. 

Certain defunct brands are worth buying ,  but I just wouldn’t with Blue Circle. 
 

Sonic Frontiers, different story as Parts Connexlon still repairs and mods them.  
 

Wow , that place has exclusive repair for many good brands...good to know .  Most of those brands listed are still in business.  

BC made some great sounding gear. No doubt about it. Good value used if you pay 25-30% of retail at most. Why? He built the amps with copious amounts of white epoxy holding the electrolytic caps in place. This goop covers all the caps and connections to the caps.

These caps do age and will need replacing now. What a major hassle to try and work on these now! This is enough to keep me away from the power amps.

The preamp in question is much easier to work on. He still used a clear epoxy to hold the caps and parts in place, but the goop is not everywhere like in his amps.

Any good tech can work on the preamp as the circuit is straightforward. Replacing the old electrolytic caps is still going to be a bit of a hassle with the epoxy build design. It can be done, but a hassle. These caps will need replacing as they are now some 19 years old! Figure this into the cost.