Hello and thank you for taking the time to read this. My husband and I are new boat owners. We have a 1972 StarCraft with a Mercruiser 120 I/O. We were out enjoying our boat one day and the engine started making a clunking noise. We stopped and rowed into shore. We figured it was the lower unit gear oil that was the problem and it was... chunky and gross. We refilled her, started the engine and she ran great! However, it does not shift into forward or reverse now! It just glides from front to back easily, but does nothing. Any ideas?