Hi Richard,
I posted a reply here some years ago in response to someone elses query on the very same thing, after replacing my own original unit. (with photo’s) I don’t have the details to hand right now but it should be on here somewhere.
The original unit, 40+ years old at the time, was seized up & was going to cost a significant amount to service, (@ £40+ p.Hr) so I wrote it off & bought a Vetus unit & St/Steel wiper arm. Total cost IIRC was around £130.
Cheers,
Jeff