Stupid gasket question

[Sir Brixalot]

This sensor was leaking. I've got a Beru which can with a gasket. The old one didn't have a gasket at all. I can't seem to get the sensor back in with the gasket on, I'm assuming the gasket goes on the other end. Is the gasket always used?

[Oldiebut goodie]

O-ring? Is there an old one caught inside? - I have been perplexed before when that has happened.

[Sir Brixalot]

Yes it's an o ring. I'll double check. It's too cold be by soaked in coolant but might as well do it properly although no leak after a longish drive but it'll only start again if I don't change it.

[itchyfeet]

The old one must have had an o ring to seal, as said If you think it didn't have one it must still be in the hole.
check if it's a VW housing (VW part number moulded in), some budget aftermarket thermostat housings have a slightly larger aperture and may tend to leak.