Is the undercarriage that bad, I'm looking at soft dirt and clay to clear some land for about 500 hours, it shows about 60% left.
What size of machine are to talking about? The biggest problem I saw with it was on D6T size machines and it was the seals in the box sections leaking oil. That usually happened in the 1,000 to 2,000 hour range and it happened on three or four box sections at the same time. In those days Cat was offering a discount on new chain assemblies based on the actual wear on the rail sections of the links. I don't know if they still offer that but I would also assume that the assemblies have been improved since those days. Soft dirt and clay materials is pretty easy on the running gear.
The first and second iterations of System One had the problems noted by @John C. I believe this is where the bad reputation comes from. The later ones seemed to be trouble free for the most part. Over tensioning the tracks or constantly running LGP machines on rock still causes early failure of the seals. In my experience, after the second generation, treating them with the same care you'd give a normal undercarriage caused no problems and gave the advertised life. An added benefit is no extra wear in reverse.
the system one undercarriage was replaced last year so it's got about 500 hours on.
So we can understand what you are saying, you have 500 hours from new on the undercarriage and you are already 40% worn overall on the undercarriage. Is that correct? What machine model do you have and do you have the milage it has traveled since you installed it?
Sorry was looking at a different D6 it's 10k hours but the UC was replaced 500 hours ago with a new systemone UC
https://www.machinerytrader.com/listing/for-sale/255509085/2010-caterpillar-d6n-lgp-crawler-dozers
From the photos that are posted, the sprocket teeth look good, the photos don't show the bottom rollers and one of the front idlers may have wear dents from the bushings and that may indicate that only parts of the undercarriage were replaced. It is common among sellers to replace chains and pads and nothing else and call it a near new undercarriage. It is also common for failed chains being replaced and a discount being applied against the purchase of some new components.
It looks to me like they may have replaced the chain only. Sprocket teeth and idlers appear to be older. As I understand it, System One was designed to wear out as a complete set, meaning the sprockets, idlers, rollers, and chain all wore out at about the same time. This held true for the non LGP units we had. I see the one listed is an LGP so it's possible they ran it on rock and the chain wore out prematurely.