I agree 100% that you should remove the trim and expoy it over, west systems are great products and I would highly recommend using their epoxy. I would still put the trim piece back on to give it a nicer finishing look, and to add to water prevention although if done right it should not occur. As mentioned above, It might be a very good idea to use a moisture meter to check for a wet transom before going through this work, if there has been some rot, it will only get worse and no sense stopping what has already started if that is the case, you will need a full fix not just prevntion at that point. As for the stress crack, drill the 2 corners of the stress crack, drill in reverse when going into gel coat or you will chip it badly and make it worse. By drilling into the 2 ends you will prevent it from expanding, only reason it would expand more is if you had a major water issue and your transom begna to expand in size. It is not uncommon to have cracks in gelcoat, especially around the transom since this area flexes the most and gets a beating, gel coat is not very forgiving so it becomes brittle and cracks over time, fiberglass below will not, but the gelcoat is protecting your fiberglass below, so any source for water can damage the structure over time. You may not be able to make it look 100% perfect, but if there is no moisture in the transom which could be very possible, drill the 2 ends as I mentioned before, and give the area a quick sand once over, and then call your local Grady dealer with the year of your hull and they can get you a matching gel coat repair kit, it will not look perfect but will be very close, likely only you will know it is there if you examine it closely but others who come aboard will never notice the difference. Coat over it with wax once it has cured and dry and your set.
If you plan to drill a hole to check, you want to start near the bottom and typically on the side where the crack is, the water typically settles down, but does not always work its way that far down if it has just started, so holes near the crack itself might be needed as well. These holes will need to be filled with west systems epoxy as well to seal them up and then touched with gelcoat to restore it back to near original condition, and then repaint with bottom paint in these areas if it was there to begin with. I know drilling holes are scary, but a moisture meter is expensive, so unless you have a yard near you who owns one and will come out to check the transom or will let you borrow it, drilling holes might be the only sure method. The transom may sound solid or look solid, but I've seen plenty of transoms that looked great on the outside but were a nightmare when drilled into and checked.
