that plug is a cold start aid - a glow plug and there is (IIRC) a fuel connection to it to drip hot fuel into the intake. On mine it was never connected. I played with it once to see how it worked but did not do a permanent hookup. No fuel drips unless it is connected to +12V to heat it up.

There should not be any "delicate" parts to deal with.

Sorry you had the trouble.

Dave's suggestion for a bullet proof anti siphon is a good one IF AND ONLY IF on your boat the scuppers do not flood when you are heeled. On my boat that can happen. The end of that tube must never be under water. That tube will weep a little water when the engine is running so your design must accommodate that.