That's absolutely true. In 1984, I rebuilt the alternator in my 1981 Buick Skylark. Most of the parts could be had at the local parts store. Nowadays, that stuff is only available mail-order. But, thanks to the web, the parts can be had, altho you gotta wait a couple days.Rebuild kit? LOL they are harder to find than the cylinder itself. We don't fix sh!T anymore, just replace parts. Try to buy a GM starter solenoid for a vehicle with plastic bumpers....Or an alternator rectifier bridge and bearing kit. AC compressor clutch...Etc...Etc...
Still, for the trouble, it's usually easier to just buy the re-built part. $37 for a brake cylinder versus burning an hour going to 3 parts stores trying to find parts to rebuild one is a no-brainer for me.
And, FWIW, I've done nearly the same thing, but was fortunate not to blow it apart