Ask yourself how old is your MK 25 ?? Its at least 60yrs old could be 62. Your internal parts are not new. Kiekhaefer back then said 1/2 pt. per gal. or ( 24 to 1 ) If you want it to last a good while do that or go ahead and seize that one then look for another.
I would use Mercury oil, But that"s just me. Gearcase fill with 105. Some complaints changing grease but light heat from a heat gun to warm the aluminum & will exchange. Can’t think of it but cornhead grease too, getting old.
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