I bought a 55 three years ago with 8,000 hours on it. I've put an additional 600 hours on it and its been running great. Twelve row corn planter in the spring and 840 bu grain cart in the fall. Very dependable, however, the hitch is too small for the cart and we have broke two of them now. That could be because of the man I used to have running it though.
I took it to Cat for an annual last winter and told them to run the overhead and check the main/rod bearings. They ran the overhead and told me it was fine and they didn't bother with checking the bearings because those motors don't go through bearings. In 600 hours, I've never had to add oil or coolant between changes. Mice do like the cab though, I haven't been able to stop them from getting in. I went with the Outback autosteer and their BaselineX for RTK. I'm not impressed with the steering on the tractor, its not fine tuned enough for small corrections.