There was a time that many industrial companies has repair and service depts or pools. They would repair anything. I have experience with Hughes and AT&T. These service depts went out of favor with localized cost/benefit accounting. Eventually I believe it became impractical to do in-house repair even if information was available. It is a sad note to this type of technology.
Anecdotally, I recently attempted to repair an Epson Artisan 837 AIO ink jet printer. I found the complete service manual online. After 9 hours of disassembly, I had it back together and working as before. But I didn’t fix the problem. Printer price ~$300. Age ~4 years. Epson estimated service $300. My time value according to my wife ~$500. My conclusion, buy a new printer, recycle old printer. Do not repeat exercise.
Should this be applied to test equipment? I don’t know. I am conflicted. An Epson printer does not have the attachment that my HP 54503A scope has, but it is fundamentally less repairable than that Epson printer.
Tek was not the only Co to go dark. HP, IBM, Fluke, etc joined them. It is as if we, (boomers) got anchored in time and expectations while the industry we loved evolved without us. Just my reminiscing.......