Well, I called Madsens again this morning and talked to a tech. He told me that their guy that rebuilds Silveiy Jacks was on vacation traveling the world for a while but he always told guys to always use the Silvey Tree Saver oil. Mobil DTE 21 is that oil, just sold as Silvey Tree Saver oil. I researched some on the DTE 21 oil and found it to be a type of Machinist Spindle oil. Apparently the DTE 21 is like a super high performance hydraulic oil that is made to withstand really high PSI without breaking down. The Madsens tech said that, through their experiences, guys who ran fluid other than the DTE 21 always had problems with seals blowing out. I asked him if there was another fluid that could be used as a substitute and he said that he was not even going to go there because of some blown seal incidents they had. He strongly recommended using the Silvey recommended oil. I ended up ordering Madsens last five gallon pale. Yeah, I said five gallon pail. The Mobil DTE 21 only comes in five gallon or larger. The five gallon pale was $100. The Silvey hand pump takes one gallon so I will have four gallons left over. Oh, by the way, I called Valvoline and they tried to cross reference the Mobil DTE 21 with anything they made and they said they could not find anything with the same properties as the DTE 21. I don't know if another oil would have worked just fine or not but I figured Madsens has been in the industry for long enough to know their Sh*t, so I did what they and Silvey recommended.