Has anyone had experience with replacing the saildrive seal ( the large rubber/neoprene doughnut shaped seal easily visible at the base of the engine when viewed from forward ) in a c&c 99 with a Volvo Penta MD2020 diesel engine. The manual suggests replacing every 7 years. I have #55 built in 2004. Have never had any problems with the seal and am wondering whether to replace as a matter of routine or to wait and see if problems develop. I sail on Lake Erie -Great Lakes-so no salt water exposure. What are other 99 owner's doing?