The Bosch copper plugs to use are either H9DC or H9DCO.

The H9DCO has a slightly wider side electrode. Some believe it produces a better spark. I've run both and cannot attest to that claim. Interestingly enough, the last set I pulled was H9DC and I got better gas mileage on that set than any set of H9DCO ever used.

Either plug will do well for you. As mentioned above, the plats are supposedly bad news in 103 motors. It isn't so much the motor, but the CIS FI system(according to info posted @ this site).

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"