JWB53,
I have a 2004 B series with about 1100 hours now, and thought there have been a couple issues in general they are durable and reliable machines.
Biggest issue that might cost you big $ is drive motors. If they haven't been replaced already, you will want the dealer to do a thorough hydraulic flow test which can detect early signs of motor troubles. If you search this forum you will find a lot of info on that issue. If that Toolcat has more than 1000 hours on it, most likely it has had motors replaced (there are two), will be exhibiting signs of failure, or has motors which are not part of what appears to be a faulty batch from Comer. Paying out of pocket for that repair could range from $3500 to $8000, depending on if the hydraulic pump is damaged by little motor bits floating throughout the system.
Other that that problem, the only other issues I have experienced are wire routing problems (which tend to show up within 500 hours of use) and hose failures, which at 1100 hours I'm chalking up to normal use, though I have routed / tied replacement hoses differently to reduce chafing. That stuff, while annoying, is not nearly as expensive as the drive motor failures.
I'm a little disappointed in the paint on the bed of my 2004, there does not appear to be a primer under the white paint, which peels off in large flakes. I don't salt with my Toolcat, so it has never been exposed to anything more than water. Front boom paint seems very durable, just the bed that I have issue with.