Re: OMC Stern Drive
If you remove the upper drain plug (right side, ~12" from top) the oil will typically run down the drive all the way to the skeg. To make the job clean, stick a piece of duct tape (2" wide, 4" long), just below the plug, pressing down only the top ?" or so. Turn the lower corners of the tape into a vertical loop and stick it to itself. You now have a "funnel" that will direct the draining oil away from the drive and into a container. Remove the upper fill plug to allow air in for faster draining.
Now you can remove the screws from the top cover to have a look at the gears.
If a tooth is missing and you replace the set, it's a good idea to also replace the roller bearings and seals. I got all the bearings and seals at a local bearing supply for less than $100.
30% wear on ball gears is no problem, I wore mine down to over 50%, then welded them with hard face rod. They lasted for many years after that, and I run a performance 350, 300hp+ on a 19ft Glastron.
