One of less pleasant things we originally found on the boat, when we bought her, were some incontinence pads. We thought they were there to catch water from leaks (we found that mostly these were from the windows, but also some from mooring cleats and other deck fittings).
However, I’ve just removed some plywood that was bonded to the hull as a sloped part of the floor as you enter the aft cabin. The plywood turned out to be saturated in diesel. So maybe the pads that were under the floor of the aft cabin were to absorb diesel.
We think that the diesel tank, on the outboard side of the corridor to the aft cabin, must have had a bit of a leak. The plywood covered a section where the grp covered foam stringer was cut away. This left a bit of a groove that the diesel must have run along.
It is well over a year since we removed the diesel engine and fuel tanks. Hopefully this is the last bit of diesel impregnated wood to remove.