I just performed this repair on my 126 car. I have no idea how anyone could use a "nut & bolt" approach. There's no room in the sliding area where the bushing goes for the bolt head and the bushing.

I went to Home Depot and bought a 2" long - 5/16" clevis pin. I cut the pins length so that 2 holes remained. I ran the pin thru the hole in the bushing, slid the bushing into the rail, affixed the arm to the end of the clevis pin, then secured with a cotter pin.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"