Need help identifying rubber seal found struck in thermostat.

[Shsrebel67]

I recently had oil get into my cooling system so I tore the truck down and done a head job and head gaskets. When I took the thermostat housing off I found what looks like some sort of rubber seal hanging halfway through my thermostat holding it open (which explains the check engine light for low coolant temperature) the seal was torn in half and hanging half on the water pump side and half on the top radiator hose side. As you can tell in the picture it is missing a couple little pieces. I have searched everywhere and can not figure out where this would have came from. Can anyone help me out here? Pictures of the rubber piece are attached.
2012 Ram 1500 5.7 Hemi 169,000 miles.

 

[Green_Manalishi]

Radiator cap gasket?

 

[Shsrebel67]

Nope I compared the old radiator cap to a brand new one and the thermostat to a new one and it came from neither of them. Due to the water flow direction it would’ve had to come through the water pump or out of the water pump to make it to where it got if I’m understanding the schematics right. If it came through the pump it would’ve probably eaten it up.

 

[EdGs]

Man, that is crazy!

Too bad you don't have a pic of how it was wedged in there.

 

[seems fishy]

I wonder if that is rtv gasket silicone.They used it instead of a gasket and some of it got into the thermostat