On Tue, 03 Aug 2010 18:33:58 +0200, Boeland
wrote:

My steel diesel tank has developed a small hole due to rust. I can't
take it out of the boat without removing the engine. Aside from this
pin hole the tanks looks in good shape. Have any of you used some sort
of coating on the inside of diesel tank to plug the leaking hole and
prevent further leaks?
Thanks for your recommendations.

You can probably do an emergency repair with JB Weld and Duct tape but
things are going to get worse sooner rather than later.