I have been using Castrol DOT-4 for a long time. The containers used to be white. Bought the newer Rover and the specs were synthetic fluid for brakes, so I looked on line and ordered the new stuff in black container. Well, when I compared them, it was the same old Castrol as the white containers said synthetic too, Mixes well with other fluids, not the same as DOT-5 which is totally different. The Castrol is compatible with rubber or neopreme seals. Has a pretty good temperature tolerance. That is the only brake/clutch fluid in my shop.