Re: Yanmar 2QM15 return fuel line leak
James, that's pretty nasty looking. Looks like you're getting salt water on your engine, and that's likely why the line failed. Makes no sense that it would corrode from the inside out, nor does it make sense that it eroded, since the fuel velocity in that pipe should be pretty low.
That return line connects the low pressure and high pressure sections of your fuel system. It routes excess fuel from the injectors back to the fuel filter at the injection pump suction. It should be robust.
With the fuel return pipe off, you should replace the hose clamps on the cooling water hose in just aft of the pipe, and check that hose to make sure it doesn't have a crack in it. It is a molded hose, but you can likely replace it with an unmolded hose. I'd look for other leaks, perhaps from the zinc plug in the front of the engine, and the hose from the raw water pump to the small distribution manifold where the zinc is installed. Have you been replacing your zincs regularly?
Check Torresen Marine's web site for part availability. They have accurate status for part availability. You can call them for pricing, but you'll have to buy it in the region you are in...they can't ship outside their region.