My key wont go backwards anymore, I tried a new spare key but that doesn't help could someone point me to some info on replacing the key lock cylinder and where to get a new one (I've got a 90 bonneville)?

In case your wondering, I like to eat out in my car and listen to music, if I put the car in "on" mode, it'll run down the battery really fast unlike when the key is turned backwards.

You may want to try a quick couple shots of graphite powder. It is a lubricant for door locks and lock cylinders. Then work the key a bit..see if it solves the problem.