Checked things prior to a 360 mile round trip and noticed brake fluid reservoir a bit low. Surprised as pads are recently changed and it was OK then. On way back the level warning light started coming on and gradually got more frequent, when cornering or braking. There are no external leaks so all I can think of is it's going into the servo. The brakes work fine and there's no obvious effect on the engine.

I'd be interested if anybody has had similar experience or can make any suggestions.

The clutch shares the same reservoir for it's hydraulic fluid - any leaks or issues in that area?

Good point, I hadn't thought of that. But I don't think so, there's no sign of any leaks under the car, and I assume there's a drain hole in the bell-housing. I'll have a better look tomorrow.

Thanks

any signs of fluid on your carpet in the drivers footwell?

I don't think so, but I'll check tomorrow. The brake servo and master cylinder are on the left side. I've had no occasion to locate the clutch master before now, but I will! From the Haynes manual I think it's probably on the right.

The clutch master cylinder is located on the clutch pedal

Yes thanks, found it, you can only see the pipe coming through under the bonnet. But there's no sign of any leaks there or anywhere else. Still puzzled, I'll have to keep my eye on it and see if anything develops.

did you have an airlock when you did the brakes, you might be low and the air bubble came out, hence the fluid level appearing lower?

No, I didn't open any bleed screws, just pushed the pistons back and kept an eye on the reservoir to make sure it didn't overfill. Ended up between Min and Max no problem. That was on 21 Jan ready for MOT.

Update on this. Got the car over a pit and it turned out it was a fluid leak, from a corroded pipe. Most of it caught by the rear subframe which is why it hadn't reached the ground. Fixed it with a length of copper brake pipe. Quite impressed by that as it's first time I've used it. It's very easy to bend, and the routing was awkward, it would have been all but impossible with steel pipe.

A bit annoyed with myself as I like to smear steel brake pipes with grease, but I'd missed that part, above the subframe. I should have been more diligent! Of course not everybody bothers doing anything but don't have a problem, so there you go.

Thanks to everybody who posted.