I've just bought a facelift 120 Multi, and the brakes were truly butt clenchingly awfull, the discs were worn deep but had new pads.
There were deep grooves on the edges, meaning the pistons would have already have extended out quite far, so corrosion/dirt could have entered beneath the rubber boot onto said piston.
Anyway, suspecting the calipers were sticking, I removed the pads and pressed the brake pedal to extend the pistons without them coming out past the seals, then pulling the protective rubber boot down and giving the piston a good clean and a greasing, as well as twisting the piston in its caliper.
For me this did the trick as they were indeed sticking when the pistons were almost fully in ie with new pads....
To finish it off, I bought mtec drilled, grooved discs and mintex pads, they are a little bit noisy but definitely worth it, as I don't now have to jump on the brakes to stop...
I personally dont feel the need for braided hoses at the mo, but would definitely consider them to replace old worn out rubber.
The multi is a heavy old bus and in my opinion underbraked, I've had 4 and they all braked with lets say, leisure...
It may be overkill, but I have considered in my dreams, ie will never happen, putting in a nice set of uprated calipers, (Red Brembos), if you ever work on the standard calipers you will see how weedy they are....