Ed, If you have loosened the set screws and it still will not move, I would suggest using some penetrating oil for a few days; applying ever couple hours. The stock molded material has dried out over the years and the two pieces have gaulded together. Good luck and keep us posted.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7