My cap came off 5 years ago, when new. Luckily, I discovered it before any fluid caught fire. Until last year, when I bought Craig's cap, I would check the cap almost daily. There are several ways to accomplish what his cap does--probably cheaper, but the product looks good and definitely takes care of the problem. Great peace of mind with it on. The cap has never twitched since the install 14,000 miles ago. I used to have the cap on so tight before that it took a pair of 440s to get it loose.
Great product, looks good, well worth the cost, and made by a fellow MCVO member. I believe they are sold through Archer and Roe.
Steve