Expect you might get a suitable response if you post over on trailersailerplace. See previous posts on there which don't answer your query but could be of use. Suggest correct typo in your post subject line - Banks 80 to Binks 30 which you have in the post text.

www.trailersailerplace.com.au/phpBB3/viewtopic.php?p=225228

www.trailersailerplace.com.au/phpBB3/search.php?keywords=lift+keel+hydraulic+oil&terms=all&author=&sc=1&sf=all&sr=posts&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

Assume you have this document which doesn't answer the question but maybe others.

johncrawfordmarine.com.au/advice/trailer-sailer/farr-b-30/523-farr-b-30-information-overview-compressed/file

How old is the boat and hydraulic system for the swing keel? It could be better to renew the whole oil volume so expelling water and air and other probable contaminants, including a flush out. These links could be of use for your top up or full renewal including flush out..............bleeding the new system would be needed.

www.boathut.com.au/product-category/steering/hydraulic-steering/

www.boataccessoriesaustralia.com.au/hydraulic-oil-15-grade-1ltr

Rightly or wrongly I have been using this in a backstay adjuster and it was all I could get at short notice.
Seems to be working fine.
www.repco.com.au/oils-fluids/specialty-oils/hydraulic-oil/penrite-hydraulic-jack-oil-500ml-hjo0005/p/A9391333?srsltid=AfmBOophxRq5lUgeRZyRMWqnyylZcOMlc9oUHui4JIrY-ss6SOlhggUm