Question about hydraulic steering fluid

[RALPH BERGER]

My 1979 Tollycraft has soft steering inside the cabin.  The wheel has written on it Oil - ISO Shell Tellus #10 or ISO Chevron EP Machine #10.  Most hydraulic fluid I can find is ISO 15.  Is that acceptable to use?  Or does anyone have a recommendation of oil to use?  Specifically, is the Marine West product okay?  Thanks in advance, Ralph Berger

 

[ken]

If you have "soft" steering inside what about the flybridge? Usually caused be a leak somewhere. Dealing with that right now,. Seastar unit leaking like a sieve. Type of fluid is kind of mute way past warranty, I don't think you can do any damage by using the "wrong" type of fluid.