3M 5200 was formulated to be an adhesive not a sealant, and really not a should not even be sold to anyone other than those in the marine trade. It was developed as an adhesive and for years, and probably still is, has been the go-to adhesive for securing decks to hulls. The reason being it doesn't come off and the only way to remove it is to cut it off.
I have seen lamination on fiberglass boat decks and hulls destroyed by trying to remove a deck fitting or thru-hull that was bedded with the stuff.
For a long time the sealant of choice was 3M 101 but when the government(EPA) stuck their hands in the boatbuilding industry, anything that was labeled "poly-sulfide" was removed from the market. The polyurethane sealants came to the fore-front and 3M came up with a sealant called 4600. it was a disaster and many of the tubes of the stuff hardened on the shelf. 4600 went away and was replaced by 4200. There are two versions of that, standard and fast-cure. I've used the fast cure to bed thru-hulls on fiberglass boats with no bad effects. it's good stuff. I/m sure the standard stuff is good, it just takes longer for it to cure. With a proper installation, the useful life of the polyurethane sealants seems to be around 7 or 8 years. If it's in a critical application i.e. below the waterline, it should be removed, the surface cleaned with acetone or KEH, and the fitting reinstalled with fresh sealant.
West Marine sells their store brand of polyurethane sealer called Boat-something, can't remember the name. It's probably about the same as the 3M version, but 3M is one of those companies whose product, when applied properly, does exactly what it is intended for. I have never felt a need to try anything else. They are right up there with Blue Sea, Ancor, and Marinco.
Silicone is probably the worst sealant to ever be introduced to the marine industry. The working life is short when used on the exterior, it can not be painted over, and the residue is next to impossible to remove so you will not get a good seal if it's reapplied. Stay away from it.

Glad I read this, because I was fixing to use 5200 on my through hull fittings. I think I saw some 4200 at academy the other day.

Today, I decided to remove the fittings for the splash pan drains. When I removed them, I found that there was a powdery substance coming out of both holes. I am assuming that it is the wood decomposing. I felt them and they felt dry. Tonight before going to bed, I went out and checked on it. I put my finger inside and they were wet and mushy. Enough so that I could push them in with my finger tip.

I had gotten a little confidence about this working but now I have a sickening feeling about it. I'm not sure whether this would be normal from moisture rising through the transom finding a way out or whether their being mushy is a sign that this isn't going to work. Trying to decide on what to do next. Do I continue with the process and see what happens or is it past that stage and now I need to start planning on a repair.

Continue the drying process..

Hey Bobby, I have a 2005 champ and 198 which is composite and I'm going through the same thing right now. Just wanted to let you know that you're not the only one fighting this. My problem is going to be trying to find where this water was getting in at and having to pull every dang fitting and redoing them.

Sorry to hear that. We had changed all the lower fittings already so I know what kind of pia it is. After posting last night, I say and thought about it that area was dry when I opened it. It became wet after the lights were on it and it was open so that should just be part of the process. This sitting around waiting is stressful

It is stressful.
It will be fine, sorry it can't be quicker, if there was a better way everyone would know.

Mr. Goff is there any way to cause damage during this heat lamp process?( If the hull/gel coat gets too hot).

No.
You have to vaporize the water and let it escape. Heat lamp can't damage the fiberglass.

thank you for your help.

Yep 5200 is forever. Any pictures of this, I think it would be very helpful to others in the future if they have to do this. Your champ is not the only one I've heard of having to go through this process, know of 1 charger owner that had to heat the transom also.

I re-read the thread and now I have a different question. On Bobbys boat he can take the transom cover plate off and see the wood (if I read that correctly). My model has no visual place to see anything and it just has a series of screw holes, if the water is supposed to dissipate out the top, then I'm royally screwed. Right now it's dripping from the livewell overflow hole and the livewell fill hole (all 4 through hull fittings were removed). I have no water coming from the drain hole or the livewell drain hole).

Lesson learned, don't buy a used boat.

What is the best way to remove and replace them? I have been thinking about doing mine. I have resealed everything else at least once over the life of the boat.

No, I take the cover off and it is fiberglassed. The back wall is not fiberglassed closed but is sealed closed. So, I do have an area for it to escape. I also have removed the two drains from the splash pan and have gotten moisture move up through there but now they are drying out.

It sounds like you bought the right boat. Atleast, knock on wood, we won't be buying a new transom.

I took a screw driver and carefully bent the lips inward on front and back and then tapped them out. They're soft metal and will roll on you. You just have to be patient. Clean everything up then apply the 4200 inside the holes and around the new through hull fittings. Put them in and give them a 1/4 turn. There is a tool to use to reinstall the fittings which will taper one side. That's a really basic statement to give you an idea. I'd ask Goff or someone else that you trust to give a better detailed explanation or correct me if I am wrong.