Bought my 2010 back in 2014 with 168k miles (presumably highway miles being a 4 year old car). I have proceeded to put another 625k on it. Now nearing 800k miles so I have a little experience with these.
Biggest maintenance headache is the EGR system with EGR cooler, EGR valve and intake manifold clogging up. I used to take the whole system apart and clean it annually but for the last couple years I've just had the EGR valve unplugged. Runs great. Not good for the engine in theory but hasn't melted down yet. Being a 2010 mine does burn some oil, probably a quart every couple thousand miles.
It did pop the head gasket at 510k. But I caught it literally day one and pulled the head, did a valve job and resurface, went back with an oem head gasket and ARP head studs (3SGTE). Probably overkill. Knowing what I know now, maybe a felpro would have been better. I had one but it wouldn't lay flat on the block but evidently that's how it's designed. (I actually used the felpro on another Prius I bought with a blown head gasket. It worked fine) Not an expensive job but fairly labor intensive if you work slow and methodical like I do. Gasketmasters in California can come to your house and complete the job in under 4 hours though.
Front wheel bearings seem really robust. Bolt on assemblies, not a press job. But they can kinda seize/corrode in the aluminum knuckles. I replaced my fronts chasing a weird noise. Turns out the noise was the CV boots when they are cold. Rear hub assemblies don't seem to last more than 175k in my experience. Super easy to replace though. The hardest part is fumbling with the ABS sensor clip on the back side. I'm also running 10 mm wheel spacers in the rear with longer studs and super heavy 17x7 factory wheels off a CT200h (Lexus) not doing the bearings any favors.
Factory front brakes lasted 250k, rears 350k!
Couple years ago I had the inverter fail. Evidently the early ones have a weakness. I got a low miles one from a 2015 from LKQ. $200, fairly straightforward install.
Been through a couple of the fancy JBL touch screen folding face radios. Finally just went with a simpler non touch screen JBL. Wore out a couple steering wheels also. Eventually got a factory leather one.
The electric water pumps seem to be on borrowed time after 300K.
My transmission fluid was jet black at 200k. Subsequent drain and fills have been far less dramatic.
It's been the best car I've ever owned, easy to maintain and work on. Tons of used parts available. For a while parts off wrecked 2015s were nearly new but now even those are getting some age on them.
I will address the battery in another post.
