I usually take oil
samples of engine oil
and also the gear
oil. It is very common to find salt water
in the sail drive oil, which gets in through the shaft seals
. I think that the shaft seals
are the weak point in the sail drive, and they should be changed at every haul-out (every year). The salt
in the oil is very corrosive and can cause premature wear. The sail drives are a lot more maintenance
than straight shafts.
The new Yanmar
sail drives do not require haul-out to change the oil, they have a tube built in that goes to the bottom of the drive and allows you to suck the oil out with a pump.
On the positive side - the sail drive is less drag than a straight shaft when sailing.
I'll take a straight shaft over a sail drive any day.