They are great little critters, maybe not as much steel in them as a Nikon F or F2, but many of them saw professional service. If you give it a CLA, it'll last you a few decades more. The lenses are with a few exceptions great too. I think it would work well as a second camera alongside the M3. The lens on the camera is a bit younger, probably multicoated.
It's really a bit strange that they (apart from the odd rare collector stuff) don't command higher prices. The bad part about that is that I too easily buy another one... Latest one is a second S1. It's going off to Eric (meaning Mr Henderson at www.pentaxs.com) for CLA as usual.
+1 It's probably as good as the Nikon F. I'm amazed that the slow speeds are still O.K.
" A loving and caring heart is the beginning of all knowledge " ~ Thomas Carlyle ~