Get an MX or an ME Super, you know you want to!

The bearing usually goes in a tiny hole with a spring underneath, which presses it against notches on the inside of the aperture ring to provide the "click" at each aperture stop. Try holding the aperture ring to the lens and looking for the notches, which should give a hint as to where the hole is.

The two springs may well be what Sigma use to hold the lens in "A" mode, I've only dismantled Pentax lenses though and they use a pair of metal strips. Basically, pressing the A button needs to push them down to unlock the aperture ring and allow you to turn it. If you can work out where the A button ends up then you might be able to work out where the springs belong.

What a waste of what looks to have been quite a nice example!

One for people who own the gold LX perhaps?

Another one to consider for dabbling in film: MZ-10

It's a bit of an oddball with a plastic lens mount and a general feel of having been built down to a price, but it has a full K mount and supports Power Zoom (not the extra functions, you need the right Z-series bodies for those but it will power the zoom and retract the lens when you switch off). You can often pick them up for next to nothing if you just want to have a play. It was probably the top of the range of the double digit MZ bodies.

Many MZ series bodies have suffered a fault with a drive cog just to the left of the lens mount (as you look at the front of the camera). This can split leaving you with a camera which whirrs but doesn't do anything else. I managed to fix an MZ-50 with said fault by removing body panels until I could reach the cog, then putting a tiny drop of superglue on the motor shaft and moving the cog back into position. Risky, but the alternative is to do some extensive dismantling and replace the motor/cog assembly with a spare (relatively easy to obtain via ebay from the USA).

Costs nothing at all providing you have a computer - see my thread about the Hugin panorama stitching program.

I still keep my eyes open for a cheap FA 28-200mm, as I could use that on my older film bodies too.

I think you're going to need a new hood, unfortunately. That said, try using the hood with the window pointing down and see if it makes any difference not having the little cover? If it does you could always put a bit of black insulation tape across it.

I have ended up with a few 55mm Takumars, not identical though. One of them is the Auto Takumar 55mm f2.2 with a black aperture ring, which is a bit unusual in that from what I understand these were supplied with black Pentax S1 cameras. I've yet to find the matching body and suspect that may take some time!

If I see something unusual for sensible money I'll usually have a bid. I draw the line at paying silly sums for any screw mount lens though, as the only reliable matching body I own is a Spotmatic.

Looks good - you need to redo the Pentax lettering now! I've got an orange ME Super which I need to strip and respray as my first attempt is flaking off horribly.

I think the MV and 50mm f2 are probably the smallest and lightest Pentax SLR judging by the weights quoted on the K mount site.

As I've said before I think there are now people buying old Pentax gear as collectibles/antiques. For them the price is dictated by the rarity and condition, not how good the equipment is at taking photos. This lens will probably spend the rest of its life in a cabinet somewhere rather than on the front of a camera.

I have a couple of somewhat scarce lenses (K 85-210mm f4.5 and K 120mm f2.8 ) which I do use, but very carefully. The sad part is that judging by their condition previous owners barely tested them - what a waste!