As part of my plan to learn to repair old pentax stuff, I just got a Spotmatic SP, a Spotmatic F, and an SMCT 300/4.0 from KEH in "as is" condition. Both bodies were "inop", although I have yet to find anything wrong with the F. The SP mirror and aperture stopdown hangs up at slow shutter speeds although the shutter appears to work properly at all speeds. I was going to loot the SP for screws to replace some missing screws in an SPII of mine, but they aren't the same.
Here's the real killer. The 300 was labeled "aperture inop", and the aperture is truly messed up. I suspect that even if I can't figure that out my repair guru can. It's also missing the rear light baffle. I was hoping that I might be able to cobble together an SMC 300 from this broken 300 and my own non-SMC 300/4, but the full-aperture metering lug and follower mean that the light baffle isn't the same. Looking at my 300 S-T the light baffle looks like a rather complex part--not something that I'd want to get machined on a prototype basis! Where might I find a source of junker lenses and bodies from the screw-mount period besides KEH and ebay? The 300 I just bought is physically battered but the glass appears clean, so it'd be worth trying to repair if I can conjure up parts somehow. I've also got an SMC20/4.5 with front element and filter thread damage--again, about 75% of a working lens that could be resurrected with a lucky find somewhere. Yeah, I could just get a working 300, but that's a more expensive solution. DJE