How about JASO MA2 specification for oil which is intended for clutches that run in oil …
I get to answer myself when I found the answers here
https://yambits.co.uk/oils_parts_for_yamaha_xs500.html
Have you tried You tube?
Lots of XS500 videos, too many for me to view, but I notice this blue one has the same size font on the side panels as your photo of the black one.
it maybe a case of going through them as some may have the correct tank but not side panel and visa versa.