My comment was only a warning of the type of problems that are likely to be seen in a used Komatsu. The gentleman was looking for used machines and asked about the manufacturer. As far as excavators go, I stand behind what I said. They are complicated, especially for someone who has never worked on or owned one before. Komatsu to their credit did put all the electronics diagnostics on board and with some time spent deciphering the service manual a decent mechanic with some experience with computers can figure it out. The hydraulics though are extremely complicated and trouble shooting a valve or pump problem has given even highly experienced mechanics fits. Don't count on getting much of any help from the dealer or the manufacturer cheaply. I worked five years for a dealer and many times when we hit the head scratchers and requested info from Komatsu, we got the who wants to know speech.
As far as the Komatsu/Cummins engine issue goes I think Komatsu made a big mistake in using the Cummins product in their machinery. The Komatsu engineered and built engines are gold. The licensed Cummins products are a scab on the product line. While it was common for the Komatsu engines to run so long they broke before wearing out, I've seen far too many Cummins put out more smoke from the breather than the stack. This is particularly true for the small bore "B", "C" and "L/M" series Cummins used in excavators and wheel loaders. I've had power problems no one solved in both the excavators and the loaders.
The dozer line is a horse of a different color. I go back to the early D65, D155 and D375 machines and they were the hard working mules in the industry. I saw plenty of factory problems on the D375 but we made money with the one on my job site. Unfortunately we had plenty of power pod issues and final drive rebuilds by the time we got to the 10,000 hour level. They should be better now but I've heard they added lots of computer stuff. I know there is plenty on the rest as well. The early D65 and D155 machines were bullet proof. They weren't the fastest or the most powerful, but they did nothing but run day after day after day.
I have seen the price for Komatsu parts go through the roof in the last ten years. I haven't heard anyone say a Komatsu part was cheaper than any other brand.
The final problem or blessing for some is that Komatsu has virtually no resale value at all. I saw a sweet PC400LC-7 sell at Ritchie Bros. two weeks ago for $45,000.
So to summarize all this, if you are new to machinery you have a very steep learning curve. All the manufacturers are getting real complicated. Before you purchase I would suggest you line up someone who has plenty of experience in keeping them running.