I have a Kiekhaefer Mercury 1250, I think a '69. This last summer I was running it and the forward went out as we were going across the lake. Got back to dock in reverse and took it to shop. Replaced the forward gear. Took it back to lake, backed away from dock fine. Went to use reverse later in day and wouldn't engage. It works out of water with earmuffs on, however not when prop is is in the water. Did the mechanic not put something together right or does the reverse gear need replacing?