Limited production part. Proper material, wall thickness etc., molded to fit correctly. What is piece of mind worth? and consider cost of time to modify something else to almost fit.
I recently stopped a sea trial because I could see a BS auto store hose collapsing and starving the sea water pump. Not to disparage the idea of blue silicone installed competently, but not everyone is a good mechanic.
My 2c is take the $ hit and know you did it right when it's under the deck and you are underway.