It is quite amazing that a manufacturer of marine equipment
would not be sufficiently savvy to avoid corrosion
prone materials. Yet it happens all the time. My first experience was with my dive gear
bag which had a metal slider and plastic teeth. Same story as those above - it was not long until the slider was completely useless and I had to replace the zipper with all metal.
Earlier this year we replaced our dodger
which also had metal/plastic zippers (I was not the owner at the time it was installed). We insisted that for the replacement dodger
zippers be minimized in favour of metal twist lock devices but that for any zipper used that it be all plastic. The only downside that I can imagine is that the slider will eventually succumb to UV degradation despite fanatical use of 303 protectant.
Good luck to the OP - I hope that the manufacturer will recognize the design fault and compensate you for the deficiency.