My SF-600 is about 13 years old, and as time has passed, the inclined manometer has gotten slightly dirty on the inside, around the zero pressure mark(too close to the grinding room). This manometer also has had a very slight leak in it for a long time, causing the zero point to creep about 3/8ths of an inch to the right. This dirt makes setting the zero reference level difficult, as the oil meniscus is slightly obscured. It needs to have the oil drained, the manometer cleaned, and then refilled, which is not that big of a deal, except the SF manual warns that the blue gage oil is rare, very expensive unobtanium, and not to fool with it. I'm not sure I would get 100% of the oil that came out back in, and the level is slightly lower than normal now.
On another recent post, a link was put up to Dwyer red gage oil, and on the very same WW Grainger page was a blue Dwyer oil. Is this blue oil the oil that is used in the SF-600, and is the SF warning just a case of "best to buy from us" syndrome, or is the SF blue oil indeed, special?