Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-42794--1, Page 388Get this manual
3Install gasket (a) Cleaning, Inspection and Repair
Cleaning
Use good grade of solvent to rinse out tank and to remove oil from metal and plastiC partsWipe components dry using clean, lint and abrasive free cloth, or use dry compressed air
Inspection
Look at all seals, O-rings and gaskets for signs of deterioration such as swellingcracking, or discoloration
Oil Mixing Cover and Oil Mixing Valve Main Body