here are a few filter flo mechanical changes as I recall having noticed over the years(just my recollection,might not be exactly correct

1961-major revision to a perforated tub design,using dual section cast aluminum turbine type drain pump.
-~1965,pump changed to plastic housing.
-~1968,motor changed to non-servicable welded square style
-~1968, earlier counterweight changed to "cinderblock"style
-~1985,transmission case switched from cast aluminum to thick plastic.
- sometime around late'70s-mid '80s,timer went from a GE timer to another brand-perhaps eaton or Mallory.
The all-steel internals transmission is basicly reliable, but these trannys generate quite a bit of metallic particles(mostly from the brake band and helical spring one-way clutch)over several years of use and this debris packs around the input shaft seal causing it to leak.