Mark,

Are you sure the fuel is absorbed in the wood and not elsewhere in the bilge? Was the wood unfinished so it allowed the fuel to seep in? What was the source of the spill and where did the diesel fuel run. There is the "Hidden Bilge" that may be the source of the fuel smell. Check out this thread Dewatering Aft Bilge - Need Advice and see the extensive work Rich Miller did.