Hayes hydraulics use Dot 4 hydraulic fluid which is corrosive, as a result of which, when it comes time to change fluid you realize that you have to replace a the majority of rubber seals and parts in the system. There is also the strong possibility that you'll have to replace your hydraulic lines as the insides are prone to deteriorate over time due to the corrosive nature of Dot 4. Add to that the cost of any brake pads and rotors that need replacing since your last service and suddenly you find that what you thought was the simple act of replacing your hydraulic fluid is now going to cost you a whole lot of hard earned yen.
So yesterday I was faced with the possibility of yet another expensive maintenance bill plus having to order in parts and wait for their arrival. More jokingly than not I asked how much it would cost to replace the entire setup with Shimano XT Hydraulics. The answer was roughly Y45,000 and they could be installed that afternoon. Sold!
Shimano XT hydraulics use a non corrosive mineral oil as the hydraulic fluid in addition to which both their rotors and pads are less than half the cost of Hayes replacements. With regular use Hayes brakes should ideally have the fluid changed every year while Shimano's mineral oil will keep going for up to three years. If your racing with Hayes on a regular basis you may need to change Dot 4 as often as every 6 months. I've never raced on the Shimano brakes so can't accurately comment.
All in all the running cost of the Shimano setup is a lot less than Hayes.
I wasn't expecting to blow Y45,000 when I walked into the store yesterday, but next time I go in for a service expecting to pay over Y20,000 I'll be glad I did.