Hi sea rider
in particular, the Volvo 270, 280 and 290 drives...including the DP versions of the latter two, are notorious for taking in water through the o ring oem seals that go on the drain, fill and dip stick fittings. Especially if they are nipped or miss shaped when tightening up the fitting after an oil change.
I would guess that most times these drives have water in them, it’s a result of this. Many actually use aftermarket seals instead and it’s even known for some to use the mercruiser fibre seals in addition, on the drain fitting and then seal over it with silicone. I certainly used to do this. Since I first did this, it never once took water in there after in the years I had it.
when changing the drive oil on friends who currently have these drives...I do the same.
of course it’s possible this isn’t the reason...but for certain...there is a damn good chance of it.
as for how good they are...no doubt they are superbly engineered, but expensive to fix if they have been neglected. They can be a total pain to remove if they haven’t been off for a while. The retaining pins can stick solid and can be awkward. I had to make a sliding hammer with a thread fitting to remove mine at first.
you can cheat a little if the bellows need done. You can get away with just taking half the drive off.
the reverse locking catch can wear and cause the drive to lift in reverse...usually at the worst possible time and in front of an audience...haha.
The cone clutch can wear too. If it’s worn and/or the wrong grade of oil is used or water is in the oil. They can be quite sensitive with regards to grade of oil and water temperature with regards to viscosity of oil in the extreme case (the older drives pre 290, use engine oil and not gear oil).
last issue couple of issues I can think of is the trim position sender issue and the well known trim pump issue...where the ball valves wear causing the drive to drop down over a period of time and especially underway at speed.
oh and if it’s a DP (dual prop), the oem props are silly expensive. Especially the stainless ones.
hope that makes sense and all above refers to 270/280/290 in general. Not much of an opinion on newer models really.