broken rocker bolts on a 95 olds 3100.

i have had 2 sets of rocker bolts break off of a 95 olds 3100 and both times they have been on the exhaust side only. just sheared off the top of the bolts. happened after about 100k miles and then again about 5 months later after being replaced. any ideas as to why it is breaking off the bolts and not really doing any more damage? taking any thoughts on the problem....thanx