It does look as though the OEM crankshaft seal is currently NLA, which is odd since it is used across a wide range of older Volvo engines still in daily use. Sometimes Volvo resume manufacture of parts when there is sufficient demand and this may be in the process of transitioning to being a "genuine classic" part.
If anyone just has to have an OEM original there is one left on eBay Australia with world-wide delivery at not too bad a price.
https://www.ebay.co.uk/itm/255556457487
There is a brief article on Skandix which explains the differences between old and new style radial seals which could go a long way towards explaining some of the difficulties people have reported using non-OEM.
https://www.skandix.de/en/news/oil-s...ferences/1374/
If choosing a non-OEM replacement it would appear to be best to look for a conventional oil seal with a spring ring.