I'm looking at brake fluid because my car is due for a flush. I will be replacing ATE Super Blue with something else, possibly ATE Type 200. While looking at the various specifications, I noticed that there are low viscosity DOT 4 fluids, in addition to regular DOT 4 fluids as well as DOT 5.1 fluids which I understand are all low viscosity. I was initially going to go with ATE Type 200 because it has the same specifications as Super Blue, but now I'm not sure whether to go with DOT 4, DOT 4 low viscosity or DOT 5.1. Since low viscosity brake fluids are relatively recent, are there any issues or trade-offs using them in older vehicles, such as my 2002 M3? According to the manufacturers such as ATE, Pentosin and Motul, apparently not, but I thought I'd ask about this here, since there hasn't been much discussion about brake fluid.