Pentax 50mm A lens

Paul Mitchum wrote:

Just got one of these from someone on eBay. Is it correct that to move
the aperture ring beyond f11 requires depression of the button on the
ring? On my 28mm ring the button is only required for the A position.

The button lets you use the A setting. If the aperture ring won't go
past f/11, then it might be time for repair.

It's pretty clear that the lock on the aperture ring mechanism is
faulty, and gets stuck just before f11. It can be moved past this by
holding down the lock button (though I can hear a metallic click as it
goes past).

The lock button should stay down until the ring is in the A position,
but it rises after f8. What are the chances of having this repaired at a
reasonable cost, or even of doing it myself?

[Followups set]

Daniele