I had an original equipment '05 Merc. 60 hp Big Foot (CT) 4cyl, efi on my used pontoon purchase in 2016/17. Kept it up to july of 2021. I found oil/filter, fuel filter changes easy. Also impeller, plugs, and a belt were normal effort.
Replaced it with a new 2021 115 hp CT in July 2021. Plugs, oil, filters, impeller all normal effort. Checked thermostat and passages this year as I operate in brackish water. All looked great. Close to 300 hrs on it. No oil use.
Sometimes I can't hear it idling..probably my ears

...but it is quiet.
I might be dealing with a Fuel Supply Module , extremely intermittent, issue.
Single engine out on the bay, that's an issue no matter what. FWIW, ran it all day labor day, no problem....so.