I tried it in non-A mode on my K20D, and it constantly overexposed regardless of the aperture. The following pictures were taken in M mode after increasing the shutter speeds until the exposure seemed about right.
I don't think the aperture ring is functional
But in Av mode the metering seems accurate for the widest aperture, except the pictures are a bit soft.
I did buy the lens on evilBay but returning is not an option as the seller clearly stated that it was never tested. And as for trying to fix it, I opened up the mount and looked at the gazillion tiny parts inside for a lens this old. The tiny brass springs (5 of them) on the inside of the contacts seemed to be intact.
A small chrome spring attached to the ring off the aperture lever, however, was loose. I am not sure if it came off when I opened the mount. I was able to screw it back in place with a lot of difficulty and help from my significant other, who wondered why taking pictures had to be so complicated (she uses my G-9, which takes phenomenal pictures for a point-and-shoot, BTW).
The lens works exactly as it did before and I am back to where I was. A nice big, black and old chunk of metal, glass and plastic that always shoots wide open. I think this lens has some serious potential when stopped-down so as a last resort, I emailed Eric as suggested by forum members to see if he'd fix it, and will decide what to do when I get a reply.
Thanks Octav, Dave and Kevin for all the advice and help!