yeah silicone works if its clean...believe it or not normal bathroom stuff takes the heat , using it on my downpipe at the moment

Cool. Is it on a hole or instead of a gasket to the manifold?

 

I'm thinking I might just leave it and see if any carbon blocks it up. It may heal with rust and do that on loads of exhausts - can't think I'm the only one with this issue. I've tried silicone near hot moisture before (on a radiator) and it didn't work - mind you the pressure would have been higher. May check it before the end of summer to see how it's doing - still not decided.

I would leave it for a month and it'll of healed up with corrosion by then 

Cheers nige. This is what I was thinking.  You only find out about these things when you do them for yourself I suppose.  The middle silencer (also new) I can't check easily as the seam is on the top against the bottom of the car - it could be the same for all I know.