I ended up with a jar of what is labeled "O-Ring Grease" from way back. Probably from the swimming pool store. I also use it on my water ballast valves.

I add a very little to the multiprobe a few times a season when I can feel it getting stiff. You can see the various ports on the probe so I make certain there's no accumulation of grease there.

I twist the probe as I push it in. That spreads whatever grease is there and also seems to be easier on the o-rings. I've heard of a few people who have managed to replace them (M&H) but it's not something I would want to try.

Chip Bearden