I did my first yearly maintence and winter storage for the Merc 150. No big surprises.
I like the oil drain feature and oil catch around the oil filter. It made it allot more pleasant/less messy. This is my 1st motor that has the gearcase drain behind the prop. I didn't think I'd like it, but prop shaft needs to be greased anyway, and it is more a bolt than the typical short drain/vent screws. It was a very slow drain with outside temps in the mid-forties. The drain screw hole was straight, vs angled down, so easier to get the pump threaded on.
Both the maintenance and storage call for removing the plugs. ie you fog by spraying into the spark plug holes. I assume this is because the air inlet is up under the flywheel cover. The bottom plug was a little harder to access but not cusingly hard. Had to make a long extension for the fogging oil.
The yearly maintenance also calls out an inspect and test of thermostat. The OP manual says see dealer.
My serice manual hasn't arrived, so that will wait until spring.