Sorry to hear of your troubles.  First I can tell you that (having left some fuel in the tank overnight in anticipation of running again on the next day) I have seen fuel to leak from then tank (likely at the outlet) if left in.  This doesn't seem to occur during time it takes to run boat so I just don't leave fuel in it (which I know I shouldn't anyways).
As far as your starting problem, you have tried a new glow plug and new battery in the ignitor?  Other than that have you tested for an air leak?  Stick a fuel line on the inlet, open the throttle/carb and then plug the carb and exhaust with fingers while blowing hard.  You should feel pressure on your fingers and not hear/see (if you apply soapy water) bubbles escaping from anywhere.
Good luck.
Personally, my issue has been with keeping the damn pressure nipple on the manifold.  I can only imagine that the boat will run better without a nut half blocking the exhaust and a hole in the manifold!
Fortunately I'm learning how to beach the boat more consistently and not getting stalls in the middle of the pond so often.  No more swimming although I did start stripping down thinking I might have to go in when during my last rescue from a stall in the middle of the pond my boat filled with water and was just a bow bobbing at the surface by the time I got back.  Fortunately only a few drops of water in the radio box (and I didn't have to go in).  Started right up again too!