cgw
Been spending a lot of time on here!
Shutter speed of 1/8 is pretty slow, I've had older cameras not fire the shutter accurately at slow settings or bulb but work with faster speeds. Do you think it could be stuck/still firing at the slow speed? Can you get an idea by listening to it if it's slowish or fast when it releases? I'm not familiar with your particular camera or if there would be a way to get it working again at a faster speed.
Bronica ETR/SQ cameras use leaf shutter lenses, not in-body focal plane shutters. Any chance the OP can get hold of another lens to determine if it's a lens or body issue?
There's nothing inherently delicate about Bronica lenses. You may simply have one that was worked nearly to death in a former life.