They are rock solid if you make enough miles since the piston rings got changed in 2012. Try to identify when a regen is taking place and avoid shutting the engine down when a regen is in process.
The whole car is very reliable. I work for a mitsubishi and hyundai dealer, the quality difference is day and night. Can only think of 1 issue, sometimes the wiring above the interior light vibrates against the roof. remove the light and put some electrical tape around the wiring to tie them together if this happens. PHEV suffer more from this as they are obviously even more quiet.
If it was my car, I'd go with an oil + filter change every 10.000 km. Mz690070 for the filter, 5.3l Acea C3 oil.
Edit washer = MD050317