Rotaxes that have 2,3, or 4000 hours on them aren't owned and flown by a private individual. They are operated by flying schools hence the high hours. Most weekend pilots fly 50 hours or less a year. That's 20 years of flying with the same engine to get to 1000 hours.
The 2 flying schools in my area have J170s and the engines are replaced at 2000 hours, some after 1000 hours when the top end overhaul is due. Why? It is cheaper to install a new engine of the latest generation than to get the original one overhauled. The time taken for the overhaul also means the aircraft is out of service for that time and cannot be used losing the school money.
All that is required to achieve these values is the correct regular maintenance as per the maintenance manual. I have a Gen 3 3300A engine. It was the 4th off the line in 2013 with roller cam followers. I maintain it per the book and at a bit over 400 hours it runs as well as it did when it was new. Leak downs are 78/80 and I don't add oil between changes every 25 hours. I like the simplicity of an air cooled direct drive engine that can run all day at full power if required.
That aside the failure rate of 912s in the last year exceeded that of Jab engines. It may have been a oil line, radiator leak or some other minor issue but that is partly due to the 912s complexity with 2 carburettors, lots of plumbing, liquid cooling, a reduction drive and external oil tank.
The 912 is a great reliable engine but it is far from perfect and as it, like every other engine is man made it will fail at some point. A Sling landed on the beach not far from me a while ago suffering a catastrophic engine failure. The original 80HP version is considered by many as the best and most reliable. Now with the latest pumping out 160 HP from the same 1.4 litre displacement I'd be a bit cautious. Then there is the price. Wow.