wkearney99 -
Good Afternoon - Well it is a bit chilly up here in RI (19F this morning) but I made it over to the boat to take some photos of the stbd door locking mechanism. there are four photos: The outside of the door(2), the door strike and of course the inside of the door. The screws(3) on the outside just turn but nothing happens - as you would want to happen but one might ask, why are they there? When I zoom in on the key hole (remember the key doesn't even start to enter key slot) - I noticed what might be a little corrosion build up at the top of the key slot - possibly the problem. Regarding the door strike I removed the two screws not present and I did back out the larger screw / bolt until it stopped but didn't want to force anything so I put it back in to shut the door. And then there is the inside and those screws just turn like the outside ones but do not come out - interesting. The handles and dead bolt knob do not have any set screws.
It's been a while since I removed the cylinder on my door. The 3rd screw, just below the bolt, holds the cylinder into the lock mortise. The other two screws (top/bottom) just hold the mortise assembly into the door. It's a very long screw. It's possible yours has corrosion on the far side of the screw. That would explain the bolt feeling tight while extracting it. You'd be backing the corroded end into the cylinder frame.
If you've got some penetrating oil, get some onto the screw and work it back in/out. DO NOT USE WD40, as it's not very good for this purpose. Kroil, Liquid Wrench, and like are actual thin penetrating oils intended for the purpose. WD40 is not.
Note, some locks have a cover plate for the strike area, and there are other screws under that to hold the mortise assembly into the door. I never removed the mortise on my starboard door, just from the aft door. The aft door did not have a separate overlaying strike plate, it was fitted to the mortise itself.
I'm assuming you can turn the inside knob to lock/unlock the bolt, yes? It might help to exercise the deadbolt's throw a few times.
I don't recall the lock cylinder screw being problematic to remove from mine.
If I remember correctly, the handles on the aft door came off WITH the faceplates. I had to remove the inside faceplate screws and pull it off WITH the handle attached (it slides onto a square post). The handle was held onto the faceplate with a bracket on the underside of the faceplate. The inner faceplate screws extended through the lock mortise to the outer faceplate.
You probably won't be able to get the inside faceplate off until you remove the lock cylinder. The lock cylinder's inside knob should be removable, but on mine the set screw in it was rusted in solid. I suspect that to re-key the cylinder you'd have to get the inner handle removed. I was fortunate that the numbering on the cylinder (and one of my keys) was sufficient to get Kroon to make me a new key. The annoying thing is the stern door uses a Wilka key, the starboard uses a Kroon. No idea why they're not the same. But that's how "boats" go sometimes.