Thanks for the confirmation on the fuel caps Blue - case closed on that one! Regarding the discontinuation of the Automatic proper, I agree that they likely never passed the 128,000 serial. Nothing we have yet seen would suggest otherwise.
Regarding the model 4 Special and the Automatic running side by side, I keep thinking back to the ad from March 58 (see post 48792) that advertises all three simultaneously. I can only imagine that at this point they had already recognised the Automatic was destined for failure and were looking for an alternative flagship model to transition to. This same ad is also the last mention of the automatic I could find, so it probably supports the theory of a phase out.
I'm tentatively leaning towards the full 110,000 to 128,000 being Automatics with unbadged Model 4 "Specials" running from 128,000 through to 162,000. Granted a good portion of the 128 - 162,000 were model 3's. Obviously most of the Automatics were reverted to Specials as the components failed, so that just adds to the confusion. My collector friend recalled an anecdote a former Victa dealer told him - The gist of it being that dealers were instructed by Victa to revert Automatics free of charge any time they were brought in.
I did a little more digging to find out when the Special badge (the existing type) first appeared in ads and came up with this:
November 28, 1958 - Sydney Morning Herald
Supporting the theory that November was the month of the plastic badge's introduction is that this ad appears next to images depicting the first state (mock up?) badge as seen in the photo with Merv (see above). What this may show is that Specials were being sold all the way from March to November 58' without a badge.
One last tidbit for this post. According to John Mason, the introduction of the folding handlebars was one of Victa's most significant developments. It enabled them to fit the mower inside a shipping box, along with a fuel can and funnel. Notice the funnel sitting on top of the fuel cans in this image of a dealer display:
Here is that funnel, in the correct green and with its own part number: