Quote Originally Posted by Haggis2 View Post
I had a plumber mate and his builder bro redo my shower when I bought a new house. They used a white silicone sealer which looks good and is still like new 2 years later. I'll have a look and see if I can find out what it was. The only draw back is it is no good to paint over but it doesn't sound like that will worry you. I'll let you know if I can find out.
Use a silicon with an anit-mould/fungus agent...or (I don't know if this is possible in your situation...need a picture) make a mechanical seal, Ie go all exterior cladding on its are and make a flashing!