I own a 93 300sd which uses the same amp as yours, the tuner is not with this as it's a separate box below the amp. They used these on the 92 & 93 models. The part number for the amp is "140 820 00 89". I just bought one today from a San Diego junk yard for $100 guaranteed to work. If you do a Google search you’ll find places that want $550 to do a rebuild.
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