I just realised I bled my deores with reverb oil the other day by accident. I'm going to change it as soon as I get some shimano mineral in from CRC, but I just want to report that the brakes are working amazingly well, perfectly crisp and feel as good as ever! (I cannot comment on the longevity of such a method though).
It's unlikely to have any decent viscosity stability with temperature, but you'll get by in the short term. If still look to change it asap though.
I'd there reverb stuff fully synthetic? I think its likely to be, In which case your seals should be OK too.
i had to bleed my girlfriends LX brake with finish line wet chain lube whilst we on a bike tour in Spain a few years ago (we were miles from anywhere and only had bikes as transport). worked surprisingly well for the remaining 200+ miles including rocky mountain roads AND she didn't die! 🙂 reverb oil is pretty much the right stuff in comparison to that!
I've used olive oil in some maguras many moons ago. Worked fine...
(can't recall if it was extra-virgin though so maybe reduced middle class points)
Trials riders regularly used to use water in Magura HS33's for lighter action and better on-offness.