Removing 5200

I've taken off all my swim platform brackets and the exhaust tip fo give them a good cleaning and to freshen up the paint. It looks like the holes were filled with 5200 and then the bolts were pushed through. It's lasted 20 years so I want to be sure I get another 20 years out of this. What's the best way to remove the old 5200 to make sure the new stuff sticks and does its job?

The old stuff pulled of a piece of the gel when I pryed off on of the brackets , not a big deal, but I would like the new stuff to adhere just as well.

Update, found something called Anti-Bond 2015, works pretty good. It's a small bottle, only an ounce or two for $15. Spray it on (squirt bottle not aresol) and the 5200 seperates from the fiberglass like it silicone. I used it to clean up the pieces I couldn't get at with a scraper and I had a few washers from the swim platform that were glued down on the inside of the transom.   

I'll be going back with 4200, the 5200 is a little too much, I had places where the gelcoat came of with the 5200. I'm not planning on ever removing these pieces again, but just incase i need toI don't want to have to patch the places where the go.

I think 5200 probably keeps a lot of struts and fins off the bottom when people hit things. I unbolted my exhaust outlet and carved out the 5200 holding it to the hole though the hull, all that was left was 1/2 bead in a grove on the transom. Nothing to pry on from the outside so I tried hammering it from inside the boat. Wouldn't budge, I was taking good swings with a 5lb hand sledge, gave up after 6 or so because I was worried the transome might break before the 5200. I ended up having to saw it into 1/4's and then pryed those loose with a 2ft pry bar.   5200 is some stout stuff and they aren't kidding when they say it's permanent. Be prepared for a fight even with the anti-bond.