brake works fine (as in – it stops the wheel turning) but if i keep a squeeze on the lever it works its way (very) slowly all the way to the bar as if its losing pressure.
let go, and a couple of seconds later the pressure returns.
no leaks anywhere, or not that i can detect anyway.

i’m baffled 😕
(not an uncommon situation for me really!)

edit – m775 by the way.

needs bleeding

There’s an o ring on the piston in the lever. That could have perished which would explain the pressure loss.

sounds like they need bleeding to me – you could try leaving the levers clamped to the bars over night – if it is air in the system, this should get most of it up to the lever body. Then you could remove the bleed screw in the lever body and top the fluid up to displace the air. Or just bleed them.

hmmm 😕

i had them bled recently (by a pro, not by me) because of this issue, and still the situation remains the same.
that’s what’s baffling me.

Sounds like your lever’s primary seal(the one that holds the fluid under pressure when you pull the lever)is leaking slightly, the secondary seal (the one that stops the fluid in the reservoir leaking all over the floor when you pull the lever) is stopping you seeing any obvious signs of a leak.

aha!
now that would make sense.

What’d make even more sense is being able to buy a repair kit instead of binning it 🙁

errm, i’m reading between the lines and not liking it!
does that mean my brake is fubarred?

Very probably, no internal spares available. By all means try another bleed, but from the symptoms, it’s unlikely to solve it.New lever assemblies are available seperately, may be the latest models only, but can be mix & matched.