I bought a P91DC in June of 09 and love it, my favorite of four 40's. I asked about the 91 on the forum also and revhigh told me about his horrible experience also but I took the chance and it's definately a keeper. Bought it used of course and just cleaned the hell out of it and the two mags it came with and bought a Hogue for it and the old P series guide rods have some white coating on them so I called Ruger and ordered a new rod which came with a new recoil spring and also bought a new hammer spring seat without the lanyard loop. Took it out five times last summer and it functioned perfectly with Winchester and Remington but didn't like Blazer Brass but what gun does and it shoots pretty tight groups at around 15 yards but I shoot for fun and not really bent on accuracy.
I don't understand what slide and trigger work, they don't need it and $450 sounds high but you get about $80 worth of ammo and you're not going to find another 91 just sitting in a shop so if it's in really good condition and you dig 40 caliber then get it but I would still try to talk him down just to save some money.
Mags are kind of hard to find but I found some
here, it's the P94 eleven round mags. They're new and factory mags and I bought three and cleaned them good and they work fine.
The finish is in excellent condition, the lighting sucked.