The topic of running DOT 5 silicon fluid in new/rebuilt brake systems has been discussed with it seems, split opinions. Personally, I've run DOT 5 in my cars since the mid-90s without any issue whatsoever, but recently spoke to Lone Star Caliper about the M/C and calipers they rebuilt for me and they recently changed their position on the use of DOT 5 due to a high number of customer returns. They did their own investigation and determined the formula for DOT 5 changed somewhere in the 2015 time frame and it now swells the seals. I was able to find some old DOT 5 dated 2013 and older and asked Lone Star to send me a set of seals along with my rebuilt components. What I received was a variety of seals...two of which I could identify as MC seals and the other two as similar chevron seals, but larger in diameter. I did not receive any caliper seals. I sectioned the seals and soaked them in two different MFGR's DOT 5 for a week and then compared them to the virgin sections. These are the two DOT 5 fluids used. The Fade Free is dated 2004 and the Super S is dated 2013. Comparison of the various seals received from Lone Star. Interesting that the two un-identified chevron seals DID swell approximately 50% cross section when subjected to both DOT 5 fluids felt noticeably softer and more "spongy". The two seals I believe do apply to my 70Z M/C did not swell at all and there was no noticeable change in rigidity or feel. As a final check, I subjected additional sections of all four seals to DOT 3 for a week and there was no noticeable change to any of the seals as a result. I was hoping the test would be definitive by testing DOT 5 prior to when Lone Star states the formulation change took place...but it does not. Instead, to me, it only sheds more doubt on the compatibility of DOT 5 in our brake systems. Draw your own conclusions.