You should use new bolts, as they come with the blue adhesive around the threads. But I generally use stud lock, or thread lock if I do not have replacement bolts. Its a loktite product, but I can't remember the product number. I think its 472, but not sure.
If you use thread lock, then make sure the threads are absolutly cleaned off old stuff and rust free. Also degrease the threads as thread lock is anerobic, ie, it does not need air to go off, so if there is anything else around, the bond may be affected.