I spoke to David a couple months ago...he will pick up the phone when he isn't busy. It might be worth calling him after you get the SA100 to see if you can get a handle on the age of the unit and any thoughts about whether it may be time for service.
Based on all the reviews, everything David makes sounds somewhere between good and great. I own his 22a preamp and with Mazda NOS 1960s tubes, I can't really gush enough about how great it sounds!