I have had my 500 for 10 years now, and I experience breakage on my LOWER strings- usually E or A. It's quite annoying, and I have taken to buying individual A strings since they need to be replaced more often.
I think the problem is in the angle of the string coming over the pickup. I have tried sanding down the string guide, but that doesn't seem to work. As it is, I just regularly replace the strings every three months so that I won't be onstage with a broken string. (I play about two hours a week with our church band, so your playing tone should vary.)
