Looking for Help - Zenit TTL Repair of ISO setting

Hi all, I'm looking for a bit of help/advice on a (hopefully minor) fix. My workhorse for the last couple of years has been a lovely Zenit TTL, bought in great condition (from Camera House, if you're looking for recommendations).

The TTL has a dial around the film winder to set the ISO sensitivity of the light meter, a truly useful feature. However, the dial has worked loose, and the spring beneath has come out. I don't want to damage it, so was wondering if anyone here has any experience of repairing TTLs and any tips on how to get it working again! (I can screw the ISO dial back down without issue, but something has come away so that it no lonager connects to the light meter).

Any help or advice gratefully received! I've put a couple of pics in so that you can see the issue, hopefuly.

KP

Does Camera House service cameras?

No idea, sorry. Good place to get odds and sods though!

I believe the ISO dial is held by set screws and indexed by a pin. There should be a ball bearing + tiny spring for the click stops. Is that the spring you are referring to? The rewind crank threads onto the rewind fork; you need to hold the fork through the "U" and simply screw in the crank.

Edit. The dial that's off is only a handle: the part it is attached to is the one that affects the ISO setting. You would need to remove the top plate to investigate further.

That's really helpful, thanks! So I reckon the ball bearing came out when the dial came loose, as it's not there now. I do need to get the top plate off entirely but I am half way through a roll so will finish that first. I suspect 'tiny soviet ball bearings' is a niche commodity even on eBay.