Most of the worst transom problems by far occur on the "notched outboard" powered Gradys. This is because of the factory installed aluminum angle molding located at hull/cockpit liner leaking water down into transom wood core, plus lower exterior transom mounted attachments. If I'm not mistaken, you have an I/O model with a closed transom that may be only getting water into core via your cockpit scupper drains. If this is the case, I personally would not rush to have the complete transom recored before determining extent of core damage. I would first remove everything attached to outside of transom, such as trim tabs, transducers, speedometers, scuppers, etc., and then use an ice pick type probe, and/or a moisture meter to see if perhaps wood core damage might be isolated around the scupper area, or other screw attaching areas. If that turns out to be the case, and the majority of your transom core is solid and dry, then I personally would concentrate on replacing bad wood core only around isolated areas with epoxy resin paste, which will readily adhere to dry solid core and be stronger than factory original. I would get to these bad core areas by dremel cutting small section(s) of outer hull skin that are a few inches larger than damaged core area, do the core repair, then reattach the outer skin pieces into the epoxy core paste before it gets too dry. Smooth the paste so as when dried, you can sand and then paint to match hull. Reattach your outdrive, transducers, etc, and go fishing, with thousands of extra dollars in your pocket that you did not spend, not to mention time wasted.
I've done complete core replacement (
http://forums.bateau2.com/viewtopic.php?f=10&t=19949 ) first 3 pages , and it is a LOT of very hard work! I would make absolutely sure that there were not any possible viable options, or possibly a complete recore is not necessary, before committing to one. You can take a 1/8" drill bit and drill holes approximately 1 1/8"-1 1/4" deep into suspect areas in exterior transom. Check wood core cuttings that come out when drill bit is extracted to determine if they are wet or dry. If wet, they are compromised core areas, if dry they are good areas of transom core. These drilled inspections holes can be filled with an epoxy resin paste, and painted over, and if done correctly will never be a future problem. A little touchup paint or gelcoat and you'll never know they were there.
You may indeed need a complete recore on your boat, but you have nothing to lose taking the steps pointed out here to be sure you're not overkilling an easy project, and potentially wasting a lot of time and money. Just my opinion.