Bob, the 0-rings I got when ordering new have been orange. Just get the cap, rotor and o-ring and replace the black brittle one with the new orange one. It looks like your backing plate is ok. You don't mention how long the existing cap and rotor have been in place. I'm a relative newbie here but it seems like these 103 engines consume caps and rotors at a high rate.
Chuck.

__________________
1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".