I bought my 120 used, it's a low number, I think in the 200's.  It was out of warranty when I bought it but based on my previous DA service experiences I bought it anyway confident they would take care of me if something came up.  Knock on wood the engine has been AWESOME.  I can't see myself buying any other brand used unless I knew the history of the specific engine.  I've had a few DA's, a 60, an 85, 2 - 100's, a 170 and a 120.  I've had to send a couple in, sometimes no charge other than shipping to them, and sometimes just parts.  I've never paid a labor charge.  I had one of the first few 85's and had seversl problems with it.  Shipped it back 3 times and finally asked what they could do for me.  They gave me full credit towards another engine of my choice!  I was really happy when my brand new 100L showed up. You can't do any better than that if you ask me.