I know what you are talking about.. and I did see the early round and then the later oval one. Neither appear to have the lines.
That follows the CCKW decals.. except that ACKWs had the dual filters with square decals... but other than that the round->oval progression seems the same.
The early civvy oil filter decals from the S-1 filters DID have the lines:
http://www.stovebolt.com/techtips/engin ... ters/4.jpgAs did the L-1 series:
http://www.stovebolt.com/techtips/engin ... ters/7.jpgBut that went away in 1941 with the L-4 and S-2 series (41 and 46, respectively)
This is what I am leaning towards... the EARLY AC logos (fuel filter, oil filters, air filters) all have the lines... but that was changed for possibly one of two reasons: AC itself changed the logo, the Military wanted the stylized logo removed (aka the great the logo purge of 1942).
To extend that to the air cleaner: The crankcase ventilation air filter did not have the stripes. This is proven in clear photos. Since we CAN show that many different parts, on other MVs DID have striped AC logos, but that they ALSO were changed to the solid logo, it would be hard to justify the air cleaner as the sole, last decal to have the stripes. Plus, we can show that the War Department ACTIVELY went after manufacturers to REMOVE distinctive civilian logos starting in early mid 42. It seems to fly in the face of logic that the air cleaner on the CCKW would go un-noticed.
Are there decals that still have manufacturer logos? Sure. I posted the walker jack logo... The bendix hydrovac logo is pretty gaudy.. gold speckle on an MV? My guess is that removing the lines was done as a cost saving measure.... as a screen printer I know that printing fine lines is the bane of production.... they clog, the emulsion dissolves, screens need more care to keep those lines in place. Print a block character with no lines? Easy Peasy. That's just my guess.