Recommendations for Service
Annually change gear oil to look for any sign of metal filings or milky oil which indicates water has penetrated past the seals and is possibly degrading the gears.
Remove outdrive annually to check bearings and bellows for wear and potential problems and to check and grease U-joints. This simple procedure could save a lot of money if you have a problem and find out after the fact.
For recommendations on the engine portion please review recommended inboard service