a trick i used before , drill small hole in bolt in centre just enough to tap in an allen key nice and tight not too tight or you risk breaking a piece of hub off but just enough to bite ( not too big an allen key or risk jamming more ) ,heat outside hub around bolt area avoiding too much heat towards bearing seals etc
a solution similar to red locktite is used on the bolts , its melts under heat make sure you heat first then simply unsrew with the allen key dont leave too long or the bolt will expand with the hub .
are you using the correct dot brake fluid , is the brake hose old and expanding are the banjo bolts tight??
i did an enduro once ,had a stone come up and hit the banjo bolt just enough to loosen , lost the front brake totaly when i checked all it was , was a very slightly loose banjo!!