I'm replacing the brake booster on my W140. Trying to install the diaphragm travel sensor in the new booster. I can't seem to get it to go in far enough for the circlip to engage the notch in the sensor. Anybody know a trick to this? Are they usually this difficult?

I have the O-ring up on the little step where I think it belongs. It's close, but not quite there.

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Jay
1998 S320