Reflo Dart Seal

[Cal_stir]

check the instructions that came with the seal, some use a special rubber that does not require lubricant

[molotov]

nothing in the instructions that make recommendations as to what to use. I was thinking the liquid form of teflon tape but not sure.

[mark]

After an email from Reeflo I've used aquarium caulk

[hillegom]

When I think of "non-hardening Silicon material" that seals,I think of the silicone aquarium sealant that we all use to seal the corner beads of our aquariums.
It is non hardening, ie stays flexible.
Anything that stays liquid would eventually be pushed out by the pressure in the pump IMHO