David,
Some time ago I experienced water dripping on to the work surface around the sink and was initially unable to find the source. I eventually traced the source to an unsealed screw that fastened the top of the aluminium channel that retains the main hatch washboard in place. Water was entering through the unsealed screw and running down between the fibreglass of the rear of the coach roof and the teak faced ply lining, dripping out on to the work surface. Over the years the ply rotted away and I had to have the rear panel replaced.
regards
Martin