Thread: stuck zipper

just getting ready for trip to Coromandel stuck zipper on my day bag I use for reels heavy duty YK double ended but both tags jammed solid tried soaking in WD40 all day no budge seemed to be corroded inside - just tried boiling water and a powerfull spray gunk remover nah no movement any ideas ohh wise ones and yes have googled it but tapping the tags to induce movement does nothing