Super Tak 200/4 Aperture Problem

[breischl]

I just picked up an m42 mount SuperTak 200/4. It seems to be in generally good condition except for one thing. When focusing to infinity there's a bit of resistance just before infinity. When the focus is set there, the aperture doesn't work right. It will either not stop down, or it will only stop down part way. This happens in both Auto mode using the pin, or in Manual mode just turning the aperture ring.

It seems like maybe something is a bit jammed up in the mechanism. It's a nice lens so I'd like to get it fixed if it makes any sense to do so.

Is this a common problem? Is there a fix? Is it worth sending it to someone for servicing?

Thanks in advance,
BKR