Have a look here;

https://www.formgriffe.de/en/shpSR.php?p1=400&p2=308

Rink walnut grips tend to have a light coloured finish - the oil they use is from a company called Scherell.

I found 2 sources;

https://www.ballistol-shop.de/Gun-St...t_B-S_249.html

http://www.hunting-lodge.co.uk/scher...-gun-stock-oil

Hope this helps.
ATB
Mike.