I had to do this same thing almost a year ago. Getting into the tube was a bit tricky for me. I don't have any pictures or I'd post them, and as I said it's been a year so I don't remember exactly, but at the bottom of the tube is a retaining nut, but I don't believe it's designed to be used w/ a socket. It does have a slot like for a screwdriver, but the bolt coming through it is in the way. What I wound up doing was taking a removable flathead screwdriver bit and filing away at the middle of it until it would clear the bolt. Once I'd done that, removing the nut was simple. There's probably a much easier way to do it, but that worked for me.

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Doug

1984 300D 130,000 miles "Silver Blue Metallic"