Now, 504 hasn't been produced for almost ten years. Without a
serial, the
unit might possibly be 20 years old or so. So for ten to twenty
annuals,
this guy has been just fine, and all of a sudden the FAA "busts" him?
I
think there is more to the story than this.

Thanks for the response(s). So what happens when the aircraft gets
sold and there's a new owner. Is the installation grandfathered? What
would have prevented this guy from just saying, "I" built it and "I"
obviously did a good job as it's worked perfectly for x number of years.