Have searched back-posts for this. Only found 1 - which was another question!!

So - What did all you other Polo rad installers use to seal the fan switch? There is a plastic blanking plug, which could provide a rubber seal. Otherwise, I thought of using PTFE tape, as per household plumbing.

Which do existing users recommend?

Surely just doing it up tightly is enough for the plastic to seal it sufficently. Cant think the manfacturers would be applying any extra seal.

My rad switch, that I do not use, came with a sealing ring, metal of some sort, looks like alloy. I guess you could turn one on a lathe if you lost it.

Definately ptfe tape, that what we used on ours
works fine.

Thanls all, for the suggestions and advice.