I’m looking at buying a new to me boat but I have heard horror stories about the yamaha hpdi motors being notoriously unreliable and loosing power heads randomly. I was looking for more input on them. Anyone have any firsthand experience, either good or bad?

There’s 2 different HPDI motors in the high hp.  I have a 250 series 1, supposedly the weaker of the 2.  There is also a series 2 that was supposedly improved.  My series one has 490 hours and is a circa 2005 model.  It has been pretty much flawless.  I did replace a lower unit and the shop that did it surmised it was vandalized before it failed.  There was a teaspoon worth of lower unit oil in it after I filled it right before a road trip.  No sheen on the water, no puddle on the ground where parked and they felt someone drained it.  These motors require clean fuel.  I have the oil filter size water separator/filter in the bilge plus there are 2 or 3 additional filters under the cowel that need changing every other year.  Per my mechanic run mid grade fuel since they do not have knock sensors.  I now run ethanol free with a minimum octane of 87.  Maintenance is key.  I have -0- complaints with my motor.  Pushed my 21 foot heavy, tournament loaded, 1/2 tanks of fuel 68-70.  After I trashed a prop and had it repaired with some additional lift added it now runs 62-65.  It has always thrown my rig out of the hole with a 3-5 second holeshot.