I have a vibration problem on our 34' Mainship Pilot with a single Yanmar 370. Had the cutlass bearing replaced, re-bedded the rudder post, balanced the prop, and aligned the engine. Ran great for the rest of the year but the following season the vibration returned. . A boat yard recommended changing the engine mounts and stated on the Yanmars this should be done every 5 -7 years. Is replacing engine mounts a scheduled maintenance item like he indicated? Thanks!!