In the late 90's I fixed a left crank arm once. I used a block of wood and a sledge hammer. I pounded it on GOOD, then grabbed a cheater bar for the fixing bolt that had red lock-tite on it. It never moved again. At least until I had the shop do a complete install of a road bike crank set on my mtn bike.
I think the shop mechanic still is cursing the day I walked through his door.