Your probably correct in what you say about luck being a factor Dave, but overall I think the cheap nature of the camera outweighs the potential problems.
These things are solidly built, and weigh a ton, but they are assembled in a small factory by relatively unskilled labour (I presume) so there will always be the odd duff one here and there.
The Kras has a reputation for all the problems you mention, but as a cheap camera it is unbeatable.
I wouldn't spend more than $90 on one, there are plenty to choose from on e-bay, check the sellers feedback and take a chance.
Compared to a 'proper' 16mm camera like my Arri, the K-3 is an unwieldy beast, it needs a strong hand to wind it, and a tough shoulder to hold it. But it's cheap and it can give good results for what it is.
For someone looking to make a low budget movie, the allure of film is very strong, and the K-3 certainly delivers on 'no-frills' shooting.
It is a clockwork camera, same as the Bolex, so shots are limited to around twenty seconds. Once you go beyond fifteen seconds there is a noticeable drop in speed, and change in exposure, so keep your shots short.
It's a noisy camera, but no more so than a Bolex or even an Arri ST. You could try and blimp it by using a heavy parka coat or leather jacket.
Personally I'd just shoot with a guide track, camera noise and all, and dub the dialogue later. It's not ideal, but many people work this way and get good results.
The camera doesn't run at an exact sync, no clockwork camera will, but as your shots are short, there isn't going to be lengthy dialogue to shoot anyway.
Focus has been fine for me so far, but I haven't tried shooting in any extreme low-light situations with it, so I can't comment on how it would hold up with the aperture wide open.
Some of the comments about picture quality may relate to the standard zoom lens that comes with the K-3, it's got a particularly 'old' feel to it, and can make your footage look very seventies. Bit of softening and halation.
I recommend getting a few pentax lenses to replace the standard zoom. Pentax lenses in a 42m fit are pretty cheap, you shouldn't need to pay more than $20 - $50 each for them.
I have used Bolex cameras in the past, and I would say that the Kras easily holds it's own against them. It is cheaper and although the build quality might be an issue, it is worth taking a chance on one.
I have no complaints with mine, and it is a great camera to use for grabbing insert footage etc. Especially when used with a macro lens or extension tubes... macro close-ups on the cheap!
Obviously, if you can afford it, go for an Arri... even if it is a cheap one like the ST or the M, which shouldn't set you back more than $1000 if you shop around.
I do recommend trying the Kras for yourself, you might be surprised at how good the footage is, just work with the limitations in true guerrilla style