How about unsubstantiated rumors
Kawasaki, like all Japanese engines are notorious builders of strong, reliable and dependable equipment. They did have some models, equipped with phenolic cam gears that wore out prematurely...but, I think they have since rid themselves of that problem.
Kohler, also a fine engine builder, have had their problems with a relatively newer engine model, the "Courage" line. Often said "It takes Courage to buy one". They seem inherently weak and reported to break rods and/or governors long before their warranty ends. The company does stand behind their warranty and, I understand, have replaced hundreds without question. The problem remains...what do you have once the same engine is under your hood??
A few years ago, I purchase a Husqvarna with a great hydro transmission. The rider, in excellent condition, was bought AS IS because it had a Kohler Courage engine that let go at 31 hours. After reading up on forums like this one, I took the risk and bought it anyway....plus, I had a spare single cylinder, 13 HP Kohler waiting in the winds. The machine has performed flawlessly since the transplant. My wife uses it to mow 3 acres about every ten days and it still has the original blades, belts etc...here is a link to the engine swap and blown Courage: First Time Buyer & Buying Used....
You may want to take this with a grain of salt because everything I've written is only what I've heard