Yesterday, I took my boat out to do some bass fishing and to run the engine after sitting for about a month. As I drifted close to the shoreline, I put the boat into reverse and nothing. Just heard the reverse gear chattering. It seemed there wasn't enough force to engage the gear all the way in. Had to get the oar out and push away from shore until it was safe to go into forward. After I completed my day of fishin', I approached the dock and tried the reverse gear again and this time it engaged. Before I take it to the mechanic, any thoughts on what may have caused this? The weather was about 50 degrees and dry.