W6
Mine is alittle goofy too. Most times it only get really messed up when there are extreme changes in temp outside throughout the day. The fall and the spring. Summer and winter, it stays put just fine. My tires also act funky, and so does my basketball, soccer ball, and nike shox.
Mine went loose 9 months ago. I pulled them off and I've gone completely without since then. I just did a 1,200 mile trip and the vibes didn't bother me at all.
-Turd.
I bought some Delrin bar ends off eBay that have the expandable rubber core in them, haven't had any problems yet. Did you check to see if the inside of your bars are clean? Greasy might lead to slipping.