I agree with those prior that reccomend an access cover "look see" before jumping in.
The only way I have been able to address this issue without pulling the entire cap is outlined in a previous theard I posted
http://www.wellcraftv20.com/communit...ight=aquasport
It does require basic fiberglass skills and will leave a access cover with approxiate a 1/4 inch elavated lip. However, it can address a large soft spot in a deck while providing access and storage you didn't have avialable before (think battery well)
Kamikaze