Took old fuel pump apart - top diaphragm cracked, bottom diaphragm not much better looking.
Sierra 18-35437 Fuel Pump is not the right replacement for this engine. Not sure if it purports to be, but the cross reference I found listed it as one... not. Wrong cam lever for one... Wrong port orientation for 2.
My engine is A678730 - Listing Fuel Pump: 8M0073435 which is proper.
This looks correct:
https://boats.net/product/mercury/8M0073435