i finally got it loose. i had to cut the rubber under it and slide the metal tab down. so i can get a grip of the shaft under the nut. i also had to take out the overfill bottle toget a good grip on it. thanks for all the advices.

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198? 300D ???K - Future DD
1989 300TE 285K - traded in '12
1984 300SD 186K - Sold in 08
1978 300SD 330K - Died in 05