Not sure about what to tell you abou the leak repair but I'm sure you can refiberglass or whatever. In this thread earlier Mr. Andy was telling me that the square flange that the valve mounts to with the 4 screws was mouted with a clamp or something but I've looked mine over from the outside and you can see by looking down from inside the toilet it looks to be fiberglassed to the tank........But yes if you have the original collector they no longer make that type which is the o'ring type below the valve and Inland RV sells a aftermarket collector which is the glue on but you have to have that type of valve because they make both. Does your valve screw on or glued on to the collector? They have a tool that you can bore the old pipe out but forgot what it is called but I'm sure you can come up with something. I'm about to make another thread in this section to show what I had to do to my collector that I had to modify cause previous owner cut off the drain cap stub. Tell me if yours looks like mine.
"he who dies with the most toys wins"