87 Pearson 303, Yanmar 2GM20F with KM2-C trans. Purchased in 07, third owner, previous owners notes from Yanmar Seminar indicate reverse gear while sailing, stopping to engage, neutral to start. Have sailed fine for the past three years ok. Moved to new marina after launch in spring, needed hauled after being at slip a couple weeks, and noticed pink prop, zinc was good, cleaned up well, added a zinc guppy to shaft, for peace of mind. Sailed fine all summer, hauled to check and clean bottom/prop, bottom good, prop had fuzzy growth, and no sign of pink, left for 3 weeks sailing down the bay. While sailing, 4 1/2 kts and up, noticed ringing sound from shaft area, shaft did not turn, which was what I suspected at first, shift to neutral, ring gone. As the trip went along, ring seemed to increase to the point was apparent in cockpit. Only occurred in reverse. Comments?