[rickj]

I think Richard and Jon are on the correct track; I have been doing some reading and it appears that electrical current is responsible for a lot of radiator electrolysis failure (just never occurred to me, and also thought that it could not be the cause(so small a current!)-however 'expert' radiator sites list this as a major and substantial cause). Thanks everyone who responded; I am now on a mission to measure and track down electrical current and when verified rectify; then I intend to just have the tubes involved blocked off as I see no point in spending the money on yet another new radiator.