The mechanical pump is under $50 and will last decades. A marine rated pump, oil pressure switch, relay, relay socket and wiring will cost over $110.
That pump is against USCG regs
Boat motors do not use the automotive ALDL connector or OBD software
You will need Rinda software
Many things can be diagnosed easy without plugging in.
What is the motor doing or not doing?
factory serial number on spark arrestor cover will bring you back to the factory engine. check the side of the block for a builders tag if its a reman or the serial number tag on the block next to the starter
Gel changes color in the sun. After 3 decades any patch will look like a patch. Even if you perfectly match it today, in a month it will be visible as the new gel will change at a different rate than the old gel unless you redo the whole thing
