Not sure about the ICU for your 1988 560SL, but when I needed a new ICU for a 1991 300CE I learned that they could not be rebuilt (due to an epoxy over the internal components making it impossible for the rebuilders to identify the components) and none were available used. You might want to contact Beckmann Technologies (800-742-1021) and ask if they have rebuilt ICU's for your car. A new ICU for a 1991 300CE was around $2,500 wholesale ... the owner of the local MB dealer gave me a break on the price because it took their Parts Department so long to locate one for me.

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Fred Hoelzle