Water Tank Level Sensor is Leaking

I wouldn't worry too much about the ring terminal on the wire turning with the screw a rotation or two. It's preferable to avoid if practical, of course, but it's not the end of the world if it twists a bit.

Alternately, cut the wire right next to the existing connector and crimp a new one on prior to reassembling. It might be a little difficult to find a terminal for such a thin wire, though.

Incidentally, that screw head looks to me like it's a.square drive (Robertson) screw such as is ubiquitous in RVs. If you don't have a #2 Robertson screwdriver, go to a hardware store post haste and buy a decent one. It's nearly impossible to do work on an RV without one.

Maybe just replace it. They're pretty cheap and come in a pack of 3. Might be good to replace the other two also. That's one way to get your sensors clean again! :)

Thank You,
I went out drained the tank down. and tried to unscrew it.
It definitely is not tight like the other sensors. My problem is that it is not a nut but rather a rusty Phillips head screw. When I try to tighten or loosen, the wire lug moves. I tried to hold the wire lug with a pair of pliers but it still moves. I think the wire lug will break if I keep stressing it. Any suggestions?

Using a suitable small wrench, disconnect the wire. Then you can simply tighten the nut that will squeeze the rubber plug some more. Reconnect wire - done! The sensors are just a rubber plug that gets tightened down after it's pushed through the hole in the tank wall.

Have you tried snugging the screw down a bit?

Typically these are little more than a screw stud and a rubber washer/seal that is expanded by tightening the screw. I haven't replaced one myself, but it sure looks like it would be a very straightforward job (assuming, of course, the tank is emptied below the level of the sensor probe in question). If the tank is cracked or something where the probe goes in, that's a somewhat different matter.