A friend took of a cast Al fitting a while back and found the acid curing
agent had badly corroded the fitting.  I think he said he used Lifecaulk
which, I seem to recollect, is a polysulphide. 

RTV silicone cures with the production of acetic acid and I know causes some
corrosion - I have seen it.

Duuno about Sikaflex?,  but this is a right b****r if you have to remove the
fitting.

Anybody got any experiences/suggestions/

Tony of Judicious  wrote:

> Anybody got any experiences/suggestions/

Evostick Nail and Seal which is a shite Modified Silicone polymer. It
sets to a good consistency (not jelly-like, more like a butyle rubber)
it is neutral cure and it is suitable for use when permanently immersed.
You can buy the same polymer under different names, but Evostick is the
cheapest and available from large branches of B&Q. Don't get confused
with other similar sounding sealants which are acrylic, and useless.

Someone here recommended it years ago as a replacement for polysulphide
and I've found it to be excellent.