clean out your channel with long pipe cleaners,blow all the muck out at the forecourt airline,then mix 75%white spirit to 25% waxoyl ,and use one of them presurized garden sprayers,to innitiate a full coating of the area,it is messy and stinks ,sheet up well too,this should slow the natural rusting down enough to get you home before the whole car collapses in a brown heap ,

remember,the stuff has to exit somewhere,!dont smoke ! dont use washing up liquid to wash your car!it contains salt!

last nibbit of info- soap powder carries a form of ecolie,this eats away the dirt particles when combined with warm water!dont eat bold.