Hehehe! I'm not an "expert" I just happen to have a lot of different machines to look at. I started out collecting one machine for each type of item in the Boye display case, and that is why I know have two WW #9 machines, a full size treadle and a 3/4 size hand crank.
There are several people on the VSS that I would consider experts on the old machines though, and they know way more than I do about fixing up machines.