I don't know what might be in the amp that is not available today. There should be many repair centers around that could repair it. Capacitors will lose their ability to charge after a long period of time and an old amp will have the same old capacitors as yours but new ones are available.
Has B&K Stopped Servicing the ST-140?
I spoke to B&K about servicing my ST-140 some time ago and was told that B&K would not be servicing the units any longer, citing availability of parts. They recommended a new purchase (Surprise!), which I respectfully declined. I hope I am wrong here. I hope this has been remedied, but I suspect not. Someone PLEASE let me know if am wrong. I love my amp, a real workhorse and great value. I'd hate to think it's a boat anchor if anything finally goes or blows. Are there other sources for replacement parts and repair that anyone knows about? Is there anyone picking up the slack there? Otherwise, it might make sense to pick up a cheap working spare for parts scavenging. The best would be B&K being able to service and repair a venerable design.