Steve,
I have never seen a detail illustration of the overhead wiper system in any parts catalogue but my French parts book for the 15-6 does have a brief list of items for the pre-’52 wipers. One of those is part number 721081 described as “protecteur caoutchouc d’étanchéité sur support d’axe de balai” which I reckon translates as “protective rubber seal on wiper blade shaft support”.
That same part number also appears on the illustration of the later (lower) wiper system with the same part description. If you think that might be the right part CTA have it in their catalogue, their reference is 6680011.
B…………….