The 18hp does not use an O-ring on the top bearing. There is an oil recirc system that pulls any oil seepage back into the intake manifold through a small hole in the front half of the crankcase boss around the bearing (in the groove where it looks an O-ring would go). See attached pic.
Bob
1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1957 Evinrude 3022
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20
1982 Evinrude 25hp
“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."