Depending on if you haul out for winter or not..change it at the end of the season if stored for winter or every 200 hours is what Volvo recommends for my saildrive. Look for milky oil (looks like milk with a splash of coffee) which will signal the need to change lower unit seals. I just did this and it was a pain but parts were reasonable by Volvo standards. ($35 for all). If no water (milky oil) then just replace it with the recommended oil from the manufacturer. I believe Volvo uses motor oil in most if not all drives but there is a bulletin on their website stating drive and oil. PLEASE double check me on that.
What type of drive are we talking about? SC
