CRTs wear out with use, so they're only getting rarer by the day. The electronics can mostly be fixed, but the tubes can't. You can extent their lives a bit, but you're only delaying the inevitable. When it's gone (too low brightness, burn-in, bad focus), there's nothing that can be done about it to get it back to the way it was when it was new.
There was some repair available. At very least, the neck could be cut off, and the electron gun bits replaced with new.
According to the Vintage Television Museum near Columbus, Ohio, the last company in the US to be able to do this closed in 2010, and the last one remaining in Europe closed in France in 2013. (I myself don't know if there are any in some other corner of the world.)
The museum did succeed in getting a bunch of the repair equipment from the shop in France, and one person involved was even trained there, but it's been a very long process.
Currently, the equipment seems to be in Maryland in the care of a person named Nick Williams. The last update I can find from him[2] is a few years old, and expressed concern about the war that had recently begun in Ukraine affecting the supply of electron guns.
tl;dr, it may still be possible to repair some aspects of some CRTs, and doing so is apparently not a completely-lost art -- yet.
No. Repairing phosphors require complete removal of phosphor layers and re-application using basic multi step deposition for RGB strips, on the inner surface of the tube. That's not a shop repair.
