Thanks to all responders
I've been absent for a few months, but just checked in and found several replies to my questions.
Updates on Cal Cruising 36 "GEM" formerly "Discovery" and before that "Puffin":
It has been a project. Haul and survey, new batteries, bottom paint, zincs, new seacocks, new cutless bearing, new bilge pumps (2), relocated bilge strainer, replaced all underwater hoses and clamps, replaced cockpit drains (can you believe the factory used sink drains with pot-metal threaded nuts?), new hot water heater, re-plumbed fuel lines and added pulse pump and additional diesel valves and by-pass loops for ease of filter changes and bleeding lines. The installed Perkins 4-108 is a bit cranky about air in the lines. Radar soon to be added, and the electrical wiring is a mess.
The fuel tank is leaking on my boat too! I have not yet tackled that issue. I am considering a bladder inside the existing tank. I have read about epoxy treatments that seal the inside of the tank. I have considered cutting the largest possible hole in the plywood cabin sole, and then cutting a round hole into the tank top to inspect and clean before sealing. Failing that, I would then cut the tank into pieces to remove it. Then the plan would be to replace the single tank with two saddle tanks. It is a daunting thought.