Antisqueal paste is sold in any automotive supply house. It's typically a goop that is buttered on the back of the brake pad and let air-dry for about a half hour before installation.

My original pads came with antisieze paste on the back of the pads. MB sells this as antisqueal paste, which is really just repackaged copper antisieze paste. It's been reported that antisieze paste is only used if the pad backing has a circular pattern of tiny holes to act as reservoirs for the paste. It may also help to put a dab of paste at the pad backing ends that ride in the machined caliper grooves. Just don't overdo it.

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95 E320 Cabriolet, 169K