I read some other forums and blogs and the sticking is apparently common and it helps to lubricate them periodically... Somehow. Some people drilled holes and put grease ports in... Yeah, not happening.
Any thoughts?
I would be right at home adding a grease fitting...any chance of a link to that post?
Mine appears to close, light stays off, but it leaks.

I am GUESSING maybe the rubber gasket is shifted/torn/gone. I did try the flood method to flush it, filled the black tank until I saw water in the commode. No improvement. For now I have an 'add on' valve at the end of the line to contain things.
I have to bring it in to work to dump the tanks to work on it. Grandson apparently used the bathroom a few times going home. He is still amazed at the ability to go to the bathroom while underway.

The only other thing Grandpa has (in a car) that fascinated him this much are the windows in my lil' truck. Manual, crank up windows.

He is 8, and had never seen such a thing.