Craig,
My 89 is set up just like yours, with the seat adjuster located on the left side of both seats. I'm trying to replace the hinge cover on the upper right side of both seats. I ordered 2 hinges but cannot get the darn things to go on. The seat hardware has both the retainer and clips in place, but I cannot get the hinge cover to go into the retainer holes. I have already cracked one of them by trying to use a rubber mallet to force them in. Did you get yours on? What is the trick to getting these hinge covers on?

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1989 560SL