How to tighten this truss rod?

Hello, my A&L truss rod won't turn further and I'm seeking some advice. It is a through the soundhole, allen key type, and the nut is 4-5 inches long. I've removed and oiled it a touch. When I screw it back on, it turns easily until it starts meeting the tension of the neck. I get a a few turns or so in, then it stops. I need about 1mm more to get it straight. What should I try? On other styles of rods I could add washers. But I don't know if i can do that here because the rod is recessed in the hole. Suggestions? Thanks.

PS. It's not an expensive guitar so I don't mind doing it myself.