Call Garrett, they can tell you all they know about the detector, date of manufacturer, original dealer, any service and is there is any reason you should have it "serviced".
I love mine and would suggest you look at the videos. If you send email, I have a wealth of info, especially of importance is ground balancing the Infinium and how to do it for best results. Info PDF files are too large to post. There is a lot of good information on this forum, use it.
Of the four pulse units I own, the Infinium ranks second in my book.The ATX is my "best" PI unit only because of its many controllable attributes over those of the Infinium. The four attributes of the Infinium; its price, shaft, weight and that it can be hip mounted, outshine the ATX, its performance is near equal. I have many years of fond memories detecting with the Infinium. Learn the tones - HI-lo, lo-HI and their attack and sustain to improve your enjoyment. YOU HAVE A GREAT detector! Practice makes perfect.