@julianwilson
agree with your comments
I’ve been trained by Shimano as a bike mechanic, and had specific training on their disc brakes. the importance of using their specific mineral oil was always stressed
I am not stupid about commercial realities, and soon realized buying DOT and Shock / Fork oil from motorbike suppliers was 1/4 of the price of buying the same rebadged fluids from MTB “brands”. This was confirmed when I actually met a rep from one of the leading oil manufacturers and we got talking, he told me the ‘brands’ his company rebadged oils for.
yet, from talking to many experienced mechanics and industry people, it does appear Shimano have something a little different going on with their mineral oil. its not a stock item from what I can gather?
I am sure many people have had good success using other mineral oils in their Shimano brakes. But as a professional bike mechanic I’d only recommend using Shimano in Shimano brakes, and Magura Blood in Magura brakes.
For DOT brakes I’d just use any good quality DOT of suitable spec.
the reason for this is that DOT is an automotive product and subject to tightly controlled legal specifications, whereas most mineral oils are?? At least with Shimano and Magura you have a controlled specification for their mineral oils.