Where to buy brake fluid for Harm brakes???

Can anyone confirm whether Dot5 Silicon based brake oil is good to use on all RC hydraulic brake set-ups. It seems reasonable to me that it would work fine on all RC hydraulic brake systems even if they use mineral oil as standard but there's few people in my neck of the woods that know anything about the topic.

If Dot 5 is fine I could get the stuff from a Harley Davidson Dealer quite cheap.

I Bought some Dot 5 from Halfords.. comes in a little bit black bottle!

Thanks guys. Ended up buying the harley davidson brand and the local Hog bike dealership LOL. (should've worn my leathers). About 750ml for $19. Should last me quite a while.