I messed with mine for a while before just replacing it too. It is absolutely too nasty of a job to not just replace it at the first sign of trouble. I think the sand in Florida wears them out. They're not that expensive.
Valturra valves on Amazon.comMine is cable operated too. And the manufacturer just looped the extra cable in a circle instead of cutting it to length. When I replaced my valve I cut the cable to length and it works easier.
If your valve isn't working properly you risk having all the liquids leak out leaving a tank full of solids. Dropping a holding tank would be a thousand times worse than replacing a valve.