I'm in agree-ance with the guys here who've put loctite on their shift bolts. Forget about vibrations loosening the bolts, what about the temperature changes coming from the tranny? Use the blue loctite as the previous posters said. If you really needed to undo the bolts for whatever reason, the blue loctite will let you. On my lunch breaks I like to stop by my favorite video arcade. I know all the guys who work there including the technician. He uses the blue loctite on all the bolts used to hold the joysticks down to the playing panel on the machines. He said it works great and is "non-permanent" so if the game needs to be repaired, loosening the bolts is no problem.
It came up somewhere in either this forum or another, but I distinctly remember reading about someone with a Mustang having the his Steeda Tri-ax shifter coming off in his hands in the parking lot of a McDonalds!
Remember, loctite is NOT like JB-Weld. It is workable.