Just go to any Auto shop and ask for a compression gauge. Some have a solid tube as the pipe that you just push onto the spark plug hole, some have a flexible tube with a screw fitting that you screw into the plug hole. For the solid ones, make sure they have a tube with a bend in them, to get into that tioght area behind # 3 and #4.
The VERY best gear oil is Quicksilver High Performance Gear Lube.
If you're looking for a manual, please don't get anything but genuine Merc, or you'll be back here asking for explanations on what the manual means and why it left xxx bit out and does this section apply to my engine.... You get the picture.
Chris...........
