Good ones do come up occasionally, but they truly are rather rare. More common are the ones with missing parts, cracked boilers and bent frame members .... don't bother asking me how I know this to be true!?!?
Plan on replacing the main seals on the boiler, but that's not hard so don't let that concern you.
Again, in my opinion, it is not that they are especially rare, though they are uncommon ....... but the main thing for me is that they are soooooooo incredibly unique!!!