In the winter I leave the vents closed... however, anytime I open one I put a piece of masking tape across the screw. I never break this rule and have yet to sail with one open...
Ive found the fore-mentioned syringe repair to be good for delamination repairs...
There is a product called Solarize that is pre-mixed costing about $15 a tube that is re-usable and does a good job ...
Brian Carlstrom of Windance in the Gorge claims they had a 5% failure rate in 99; with about 1% failure rate in the year 2000... They must have sold lots of 99 masts, because a lot of people walked up ...