Viair 550c on craigslist , risky purchase?

Hey, I found a Viair 550c on craiglist (http://portland.craigslist.org/clc/pts/2589112223.html)
$200. Too expensive, especially since hornblasters has refurbished 400c compressors for $142.22 plus shipping, and they are nearly as fast as the 550c, but less duty cycle. So if I could get the price reduced…

What does it mean that the 400c is dust and moisture resistant (“sealed”), whereas the 550c is not? If the filter is routed away from dust and moisture (hose coming from filter to air inlet of compressor), then it’s not an issue? The compressor would be under the hood of my car and could get some water or dust on the body itself, but not thru the inlet I don’t think.

Are there replacement gaskets and other parts available for the 550c if I ever need to open it up and replace components that typically wear out? It’s a discontinued product…
Thanks

Nevermind, I found that the 550c has a fan at the end of the motor where crap can get in, and I can’t seem to find replacement parts for it online in case I ever needed to rebuild it.
So the 550c might be a bit faster than the 400c, but it’s a huge chassis, larger than the Air Zenith ob2.