I've used Motorcycle fork oil in a set of b310 struts, I used 15w20, the other types I recall were 5w10 & 10w15. I only used about half the bottle to do the 2 struts. Was a cheap upgrade when inserts are over $100 each & getting hard to find. Makes them stiffer on compression, but rebound I can't remember, as it was done for a friends car.