I agree its a great hobby and there is a time and place if it saves money. CNC would make machining even better.
My neighbor has stuff and am trucking most of a machine shop this weekend for another, I don't enjoy standing at a machine and as the nature of some equipment changed so did the needs.
As one said if you got it then it seems you need it. I have a master works for me, a genius. He was sharp enough to get something apart we were having a problem with and the first reaction was to run it down to the lathe but I snatched it up and put a DA paper on the bench and dressed a seat in a couple minutes perfect as you could turn it.
Those guys do it all the time, gonna make tool to do something and I grab a pair of tin snips and cut,,, or you could do that they say,,, hahahaha We finished the job then and there.
Back in the day a lot was built job shop, now for current equipment the parts chain has improved so much most of it isn't worth it from a cost standpoint. Even a lot of common dealer parts have become competitive.
If a guy has a one off machine a simple call from a parts manual and you got it.
I have so many tricks and stock a lot of them that there is a faster easier way,,,, and I do realize that is not the issue at hand, its more of a demand.
I can understand the knob, that could even be a practical issue considering acquisition cost + outright parts cost. We build and salvage all the time, don't have to stop everything and faster to make than get. I agree with obsolete parts in a lot of cases, a guy can fix a valve someone wants 85 for on an old fridge, its fine if it works but not worth tossing 100's at it in parts for something could be short lived anyway.