1974 Eldo fork oil

Hi, am looking for a suitable 30wt mineral fork oil for my 1974 Eldorado, having a bit of difficulty finding some, any thoughts about this out there would be gratefully recieved. Thanks.

The factory manual recommends an obsolete Shell hydraulic oil for loop forks. Can’t remember which one, but could look up. Following the supersession of that oil to a modern equivalent, and comparing viscosity charts led me to put 90 gear oil in mine. The viscosity scales don’t read directly across for hydraulic, gear and engine oils.
By coincidence, when I read Nick Adams’ book about touring Canada on his Eldorado, he also uses 90 gear oil. There is not really much damping in these forks anyway, except a little bit at the full-bump position.

Looked it up - manual calls for Shell Tellus 33, which was an ISO68 hydraulic oil. This is equivalent to 20W engine oil, or 80W gear oil, so I’ve gone a bit heavier. You can find a chart here - https://www.bobistheoilguy.com/viscosity-charts/

Thanks chaps, your answers give me something to work on, good chart. I think ill try the 90 gear oil. On bad bumps, pot holes somtimes bottoms out, but i do realise it might be the springs getting a bit tired, also that our poor roads in this country are maybe a bit too poor for the old Eldo suspension to cope with even in tip top condition.