I think it is older than a 550, I had a 4500 and yours looks like it. I can tell you if your boom swing is leaf chain driven, that is the weak link
in the otherwise good machine. And there are (2) grease fittings on the center of the front axel, one greases the pivot, the other that is often missed greases the steering bushing. I had a thread on it back in 2011. If I wasnt computer illiterate I would post a link.
I will follow along in this thread and hope I can help from time to time.