I have an HQ16 on a frame with pc-quilter that I bought used in 2010. It has been a faithful companion to my quilting. It is not stitch regulated or speed controlled, but the pc quilter takes care of that. I mention it only because I have had no problems with it whatsoever. (Most problems that I've had were operator error.) Since 2010 it has probably logged well over a million stitches, but whose counting?
It has not been "officially" serviced since I bought it. My sweet husband takes it apart and cleans it up about every 18 months, and that seems to be enough. It seems to stay pretty clean, though.