If you ran it backwards and still no release, then it is certainly stuck. If the PO didn't muck it up (like mine was), then all you need to do is take a part and clean, etc. I see you are in the rust belt like me. You'll want to hit the bolts with Blaster and let them soak a little. Even with that, when I took my auto hubs off, I had one allen bolt that wasn't happening with the hex key, and it stripped. I was able to mash down on it with vice grips and break it loose. I would not put the allen bolts back in for where we live. The manual hubs that came off a donor I had were regular machine bolts and I used them.

I haven't done an R&R on a manual hub. I would think he'll need a gasket if he takes the whole hub off?