My lower unit is making a grinding noise. I admit I hadn't change the lower unit oil in a few years and after pulling the boat and checking it right away I find there was nothing to drain, it was dry and few very small steel particles on the magnet. My question is...Does the lower unit need to be rebuilt? Would I be wasting my time by refilling and running to test? I used it gently as soon as I began to hear the noise. You guys have been most helpful to me in the past, thanks for any advise!