Debris and piston contact can score the 4th accumulator bore.
Install this sleeve and pinless accumulator piston.
Repeated reciprocation of the 4th accumulator piston causes wear at the piston/pin interface. After this wear reaches a critical point, the piston bore wear allows the piston to get cocked and gall the accumulator bore. Once this bore becomes severely galled, the accumulator body must be replaced. The Sonnax kit 34805-01K salvages accumulator housings with a worn or scored 4th accumulator bore. The kit includes a press-in sleeve, and a pinless accumulator piston that uses a PTFE guide ring to support the piston in the bore. No machining is required.
Contact a Sonnax Parts Distributor.