The clutch pedal began to be pressed difficultly and slowly to come backafter pressing (Volga GAZ-2410). 

Asa result of it, coupling joined with lateness, after release the pedal
Atcheck it has appeared that the hydro drive hose is partially corked. Thereason, most likely, is that the hose has bulked up from within because of abad mix of different brake liquids.
Also,have found out, which in the main cylinder instead of a brake liquid there was porridgein appearance reminding aluminum paint. Apertures of the piston of the maincylinder have been corked by firm sediments. In piston edges were fissures.Probably, splinters have somehow grinded to a condition of powder and/or haveentered into chemical reaction with a mix of different brake liquids. Conditions of all cuffs were satisfactory.