there is a plastic piston behind the modulator.buy a new one when you buy the o ring.75% chance it is broken.you need 5mm allen socket to remove the bolts neither of which you can see easily.good luck.

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David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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