Go to your LBS or hardware store and buy some stuff called LoctiteŽ Threadlocker Blue. We used when I was a wrench in an LBS. Coat the entire bolt in it and drive it in hard. Lock Tight is essentially a glue for bolts you don't plan on removing. The bolts should not loosen after you use it.

It could also be that somebody got confused and greased the bolts instead of using Loctite. I would also wipe the bolts and holes down with a grease solvent just to make sure that isn't the problem.