Update: My ECM had the notorious 104.942 intermittent misfire issue.
M104 HFM-SFI ECU Coil Drivers
Description: BUX127/BU941 (Darlington). Not compatible with 3.2 M104 HFM ECMs. 3.2 uses S637T. Both used to be made by Telefunken Semiconductors.
M104 ignition is very susceptible to short due to biodegradable wiring harness insultation materials being deployed by MB for these years. Updated harness is manufactured by Delphi and will have a white Delphi branding on the harness. Short in the harness, if not fixed timely and properly, will damage the output stage drivers in the ECU. This may kill output to one of your coils. M104 HFM uses a waste-spark system where one coil drives two Cyls (1-6, 3-4, 2-5). Following the replacement of HT leads, proper non-resistor type BOSCH F8DC0/4 Supers (or equiv), BOSCH/BERU coils, if you still observe an intermittent or permanent case of misfire, your ECU may need some surgery as mine did.
This W124 initially had a seasonal misfire. Happened every few months for no apparent reason. This eventually developed into a full-blown Cyl 3/4 misfire-under-load condition. Car is back to normal after replacement of all transistors. Note: Rule out any compression/fuel issues before you dive into your ECU.
Note: Resistor-type spark plugs used with OEM ignition hardware WILL cook your coils and eventually your ECU.
Note: Bosch F8DC4 can be used, optimally with 1mm gap (Beards over here may correct me on this).
For M104 280 HFM following sparkplugs maybe used in replacement to Bosch F8DC0:
NGK BCP5ES (Do not use BCP6ES - they will result in a misfire from experience)
Champion C10 YCC
BERU 14-F8DUO