There is a huge spectrum of operating practices and a huge spectrum of maintenance practices. And another huge spectrum of engine ages, and in that I include the # of years (or decades!) since the engine was last opened. Plus undeclared prop strikes, many years ago perhaps...
Put these factors on top of each other and you are going to get a huge spectrum of engine reliabilities.
The funny thing is that while cars have improved on both engine designs and the reliability of electrics (electrics used to be the thing responsible for the big majority of breakdowns), planes have not improved on the engines for many years and their electrics are generally still in the Vauxhall Viva territory. I therefore reckon that while cars of 40 years ago were truly crap (as in the Triumph Spitfire), planes probably were way ahead in reliability in those days.
The reliability hassles one gets on a plane are mostly small things - just like with a car. One very rarely gets con-rods flying out of the crankcase - same with a car.