I got hold of an ex-CC tech out in Oregon and he remembered the name of oem supplier, Knudtson mfg. Called them and the guy said (obviously) that the nut was seized on the screw. He did say they could rebuild or replace it.
It's now at Parliament Coach in Clearwater and I'm going to let them handle it. I've told them I don't necessarily have to go back with exactly the same system. I wouldn't mind if it was gas struts and raised/lowered manually.
2003 Country Coach Magna w/tag 505 Cat