I posted a problem last week - calipers seized up when hot. Turned out to be a tiny pre-load in the m/cyl pushrod. The m/cyl seals will alow fluid back so pads will retract when the seals are 'at rest' but just a few thou off that position stops fluid from returning. My pads were not returning at all so no running clearance and once hot everything seized up. Interestingly the pedal slack disappeared when everything was hot.
I've just fitted a 4mm spacer between m/cyl and pedal box so the pedal travel is a bit longer but it works just fine.
And it goes a LOT better with the brakes off!