I need to point out that when you buy Shimano parts, you support Shimano bull ****. They've created a compatibility nightmare to push riders into buying whole new drivetrains instead of just fixing or replacing a part. Of course the factory rep says that when a shifter goes, well it's time to buy a new bike 'cause yours is obsolete. Yes, he really said that to me. And the ingenious things they come up with!, like a two dollar replaceable pin every time you break the chain. Mineral oil isn't exactly environmentally freindly either, so I wouldn't sweat the little bit of hydrocarbon in a set of Hayes brakes. You make a bigger mess driving to the trailhead belching carbon monoxide than with a line leak. Which is a good reason to go Magura- Nobody I know has ever even heard of them having trouble. The Chris King of brakes .
If it really bothers you I bet you could run hydraulics with cooking oil as long as it's the proper density. The stench could get nasty after a while though, that vegetable oil will oxidize and go really rancid. Bleed your system really well.

missliz