I have an 86 Island Packet 27 with a Yanmar 2GM20F. I keep losing prime to the raw water pump. I have moved my raw water strainer down to waterline, replaced all hoses, had the raw water pump rebuilt, and I continue to lose prime. My question is, can the raw water pump get too old to effectively be rebuilt? Should I just breakdown and buy a new ($400.00) water pump? It seems to happen when I am heeled over while sailing, not when I am upright and motoring. Wits End.