I have done it on my 84 500SEL. (Door locks only). I used a kit from JC Whitney. I forget the cost but it was under $100. On my car I was able to remove the vacuum locks units and replace them with the units from JCW. I replaced the radio balance control from the center console with an old window switch. I also installed a keyless entry system. The reason I did it was because my car has orthopedic (sp) seats which uses the same pump as the locks. The pump was missing and a replacement was very expensive ($750 if i remember correctly) and I could not find a used one.

So, yes it can be done.

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84 500 SEL (307,xxx miles)