I removed the adjustment cap being careful not to drop the spring and ball (both remained in place luckily). I took the cap to my local MB dealer. He could not match the Oring with a MB part. But we did find a Volvo Oring that looked exact. And it was for the AC system, so I was confident it was of the correct material. I put it on the cap, oiled it with refrigerant oil and assembled. It went much easier than I had expected, which of course worried me because it could not possibly have been tight enough to seal. But so far it appears OK. I leak tested, evacuated over night and put just enough gas in to bring the pressures to possitive numbers.

When I finished work I went home and leak checked again. Found a leak at the compressor seal. I gassed it up amyway to make sure the expansion valve worked. It did. I leak checked again and this time no leak anywhere.. This car doesn't get used much. Maybe running it lubed up the seal and it will be OK for the season. Then next year I will attack the compressor.

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I love my Mercedes