The rear of course collects the dirty water thrown up by the front. I'd like someone to tell me how you can get down that mountain without braking. On anything this side of a parachute.
- Then use your rear as little as possible.(I assume you have mudguards)
- Hmmm, I would expect to use quite a lot of brakes, not none! But wearing through blocks? No.
- Your body IS a parachute. That's part of the trick.
Don't drag-brake; do all your braking in a big hit, almost to a standstill. Then let the bike get up some speed and use your god-given air-brake

If you're lucky you can time the dead-stops with the corners (harder in mist, obviously).
You need a little extra nerve to build up a decent speed in those crappy conditions, but I'm not talking about 40mph for a mile - in fact I haven't looked at my speedo in those situations so I can't say what speed I'd do, but it's a lot more than 10mph. I
love descending in the dry, but I'm basically a coward and do NOT like wet descents. Trust me, I take due care.
This will turn into a silly dong-waving contest soon, but I'll just say that despite not being a super-experienced alpine rider, I've descended off hills taller than Ventoux, and a few long ones in the pi55ing rain. Plus plenty of really nasty UK descents.
Brake wear issues? Never. I suppose it's possible you had some dodgy materials involved (some mainstream blocks are really rubbish).
I'm sure this a pointless
noone-back-down type discussion now, but I think this technique might be useful advice to someone reading CChat.

(I learned it from that nice engineering cycling and physics expert at the CTC - thankyou Chris!)