Joe,
I would guess your boat is similar to mine and the E27 described by Bud and there probably wouldn't be anything attached to that bolt on the outside of the hull. Do you think it has rotated so that the bedding sealant is compromised? Can you hold the threaded portion and tighten the first nut to snug it up more? Mine has a nut and washer that tightens on the hull and then two more nuts and washers that tighten on the ground wires.
As Bud mentioned, there are several theories about getting better lightning protection. There are even some contradictions among the 'experts', so the more I read, the more I get mental paralysis about doing anything. It may be that some things not done quite well enough would just blow larger holes in the boat during a strike. I've had that nasty sizzling static sound in the rigging during certain weather conditions, but so far I have not been smack in the center of a severe electrical storm, so have been lucky to date.
It sure seems the main strike's current path would like to come down the mast and there is no place to go after that mast step plate. Supposedly you should provide a large conductor from the mast to the submerged ground plate. Our encapsulated keels don't offer much in the way of a ground plate, so it would have to be external. The whole system has details which I am not sure about with our particular boat. Sorry - a lot of thoughts, but not much in the way of help.