Subsequent to this discovery of this special extra vav, I came across an article in Hakulmus magazine published in Apil 1985 entitled 'The Sefer Torah that our teacher the Rama wrote'. In this there was a photo of the Torah and it also showed the extra vav in the same word, suggesting that this great sage subscribed to this tradition also or he would not have used the Torah.
Photo of the article in Hakulmus (p. 21a). Their copyright.
There clearly was an established tradition here, and it is nice to see the Mishnat Avraham's lovely compromise.
Mordechai Pinchas