I ordered brake parts this morning for my 1972 Series III 88". The salesman told me I needed the Castrol brake fluid, or the rubber parts would be damaged. I later called back and added an item to the order and talked to a different salesman. He said I could run the newer DOT 4 brake fluid without any problems. I hope he is right because I recently rebuilt the clutch master and slave and used the DOT 4 because they told me it would work without problems.