Manual Gate Valve Maintenance

My gray water gate valves won't shut all the way off when using my tote portable tank unless I hammer on the handle a bit. Must be crud stuck in the seal slide slot or maybe they are just wore out.
My question is, are they serviceable or do I have to replace the whole works? I have the older style with the short handles that are easy to reach just under the side of the trailer.
Thanks

I think I would spray some silicone spray in and around the gate valve when the tanks are empty, that would be the first thing I would try. Not sure if your style gate valve comes apart or its part the plumbing though...

You just might have something stuck in the track that the gate slides through, that would be the easiest to fix....

If you can get to them, replacement is really easy. Just four screws and slide in a new one.

You can also do just the seals or you can sometimes get away with just cleaning out the seal groove if the seals and blade are ok. If it's not a remote cable valve, they're cheap and it's just best to replace the whole valve.

Earl