As for routine maintenance how often do I have to check/change my plugs?Boat has an hourmeter and the plugs were changed at the 20hr service by the dealer one year ago.It now has 60hrs and motor runs fine.Do I just need to hit them with a wire brush?Also what is the service interval for the lower unit oil and impeller/water pump?Engine is a 1998 Mariner 150 carbed.I use valtech carbon guard and Penzoil synthetic blend if this info helps.<br />Thanks
