sl500 et al wiring harnesses

got a 95 sl500 in my shop that had the typical broken insulation on the engine and throttle body harnesses......replaced these items but engine runs on 4 cyl`s......no spark or impulse to one coil..........traced back to a bad ezl/atk,ignition control unit...........just wondering how common is a bad ignition control unit in these vehicles........i`ve replaced harnesses before but haven`t replaced an ezl in a long time......also,very pricey.$2,600.00