About 3 weeks ago I took a look at the front pads and decided to change them. No problems; the brakes were great afterwards, no play in the pedal and I could get the ABS working even on a dry road, showing that there was plenty of braking power.
Over the last three or four days I noticed the pedal going soft, but the car was still stopping fine so I thought I'd leave it till the weekend. Then overnight the pedal developed far too much play, but I needed to get to school and back (yes guys I am a teacher, haha) but when it came time to drive home, I had almost no pedal at all. I found the brake reservoir **empty**. After refilling it I limped home at 20 mph and put it up on the hydraulic jack, thinking it must be either a failed caliper seal or a blown flexible.
NOTHING! All the flexibles are dry; I haven't had the wheels off but there is no trace I can see of any fluid around the calipers or inner wheel rims. I think I would have seen some traces considering the fluid reservoir is empty.
My next thoughts were the master cylinder. When that goes, it usually leaks down the brake pedal inside the car. At least, on all the cars I've had so far. But I found nothing. Pedal and carpet are dry.
I carefully examined the master cylinder, booster, and ABS controller but no visible leaks
WTF is going on? The only other thing I can think of is that an internal leak in the master cylinder is allowing fluid to be drawn into the brake booster and from there, into the vacuum line and eventually burnt by the engine.
Has anyone seen this kind of brake fault on the Max?

 

Update:
I took it down to the local workshop and put it on the lift. Neither the shop owner nor I could find a leak. He reckons that when I changed the pads 3 weeks ago, I forgot to top up the fluid after the new pads were broken-in. He's probably right; I can't remember checking it.
However while it was on the lift I noticed that one of the CVJ gaiters was loose. The damn tiewrap I used, had disappeared. I really don't recommend using tiewraps on CV gaiters; not after this experience. The proper retaining bands can't cost nearly as much as having to replace the CV joint.
I also noticed that the gaiters on the front struts and rear shocks were all completely shagged. Well, the hell with it. It doesn't rain here that often. When they fail I'll fit something more decent.

 

I had a similar problem. Somebody needs to invent something better for the CV boots

 

brake fluid doesn't just dissappear like that- even if you didn't bleed it after replacing the brakes. you've got a leak somewhere.

it won't take but 5 minutes to unbolt the master cylinder from the booster and pull it away a bit and check for fluid inside it. also might want to start the car and see if it idles properly while it's pulled away. If not, then it's possible that the booster is bad as well and leaking around around the master cylinder.

 

Update: I bled all the brakes (lots of air in there after the master cyl. went dry) and topped off the level. Brakes back to normal and after 1 week the level in the reservoir hasn't changed at all. Regretfully, I have to conclude that it was 'Mr Stupid' here, to blame, forgetting to top up the fluid after pad replacement and break-in. D'oh.... Replaced the CV retaining band with the genuine Nissan item, let's see how long it lasts.