The only primer leaks I have experienced is with Remington nine and a half's. My shooting partner and I purchased a large quantity of these for our silhouette rifles in the 80's. Remington replaced all of them. At the time they noted that it was caused by a bad lot of material used to make the cups. IIRC they even did a recall on several lots and replaced same.
I use every brand and type of primer out there and will watch for Winchester leaks and report back if problems are found.
