What year ? The earlier flat top fender models had no emissions junk on them while the later rounder fendered ones had a goofy DOC and EGR system. Both good tractors but they can suffer from goofy hydraulic issues like most of the 5XXX series machines Deere has made. My 5510 has had all kinds of dumb hydraulic things go goofy on it from the pickup screen plugging to the boots cracking on the external low pressure suction lines and the SCV control valves blowing O-Rings out the sides for some strange reason.
I keep fixing it and tell anyone that asks it’s given me 14,000ish trouble free hours. Who knows, maybe I’ll sell it one day but probably not. I think I’ve spent more time with it than my wife the last 20yrs so it’s kind of part of the family