Mamiya C TLR 65mm shutter running very fast

Today on eBay I bought a wonderfully cheap chrome 65mm f/3.5 lens for my Mamiya TLR. I got it cheap because there's fungus between the elements and the shutter isn't working properly. I took apart the optical assembly this evening and cleaned out the fungus, and now my attention turns to the shutter.

When I first got my hands on the lens this morning the shutter seemed to work normally but it ran very fast at every setting. The 1" setting sounded more like 1/4". Somehow during the day it got worse, and now all shutter speeds run unretarded at full speed, except B which works normally. The shutter speed ring doesn't make the "clockwork" sound when it is rotated.

I'm hoping it will be a relatively straightforward fix as I'm not great with delicate components like shutters. Has anyone come across this before? What's the likely fix?

Thanks,
Jonathan