Did you use the proper grade bolt? If to soft a grade was put in that can cause pulled threads. As far as the bolt I would just use a new one but if the threads aren't to bad you could chase them. Without seeing the threads in person it is hard to judge how bad they are and if they can be fixed/chased good enough to hold 50 ft. lb. of torque. You could easily retap to the next size though. By the way you don't have to have a hoist to change a mount I have done it in the past with a floor jack and a block of wood.