OK, I've just gotten home and played with my Volna (sounds dirty, baby).
I've found something a bit weird about my lens already. Not pressing in the pin and changing the aperture, it sometimes does and sometimes doesn't change.
But pressing in the pin, changing the aperture, and releasing the pin (like what would be happening mounted on an 88), it (almost) always springs to the correct point.

In your case, releasing the pin should always narrow the aperture, so if that doesn't happen then it's gunk or a spring.
From what I remember the last time I pulled one of these apart (which I've probably done more often than shoot with them), there's 2 or 3 springs all working against each other to make the DOF-preview lever and body-stopdown pin all work correctly. If your DOF-lever works and the body-pin doesn't, then it'll be the spring nearest to the mount not pulling hard enough. Or just gunk everywhere and the spring can't overcome the forces of gunge.
Actually, if you're in California and it's been in an attic, more than likely the oil has just warmed up enough and gooped everywhere...