Just an update. I found detailed information about the lens here:http://allphotolenses.com/public/files/ ... 40e9f0.pdf
The same site also has more pdf files some with service manuals.
I managed to get a (believe it or not) "as new" copy off ebay boxed it's absolutely spotless in terms of optics and body.
Interestingly the serial number is much later than the first copy.
I'll keep the first 28-85mm as a spare parts lens.