I have had my Cub 7235 for 3 years - bought used with 200 hrs, now have 490 hours. It has a FEL and rear mower. I have had no major problems. Have serviced according to manual. The front drive will not disengage recently. The lever moves up or down, but is not doing anything. Tractor seems to be running fine in all ranges - no strange or different noises. Any ideas?