After my last engine use, I found one of the small allen head sump pan mounting bolts had dropped to the engine room floor.  It appears to have unscrewed itself.  There is no oil leak, oil level is still good and the oil gauge was reading normal throughout the last use.  When reinstalling the bolt, should I use Loctite Threadlocker (blue or red), something else or just torque it down?  I will also go around and verify the torque on all the other bolts.  It was surprising given the engine is only 2 yrs old with about 150 hrs to date.