Thought I would give an update. I decided to open the crankcase to have a look. That requires pulling the flywheel. That requires a Mercury flywheel puller, can't use a gear puller because there is no room for the arms. So, off to Bills' Outboard in Hingham to buy one. As I'm pulling into the parking lot, BAM I'm hit broadside by a big Buick. I guess it was my failt, just didn't see them coming. Car is a total loss but nobody injured! Since I was already there I got the puller.

Got the wheel off. Even with the special ($70) puller it wasn't easy. Opened the crankcase today- again nothing obvious. Will start breaking down the cranks tomorrow. What should I look for? Any advice is appreciated.