If you've got carbon tracing inside the cap, now is probably a good time to replace it. Usually these distributer caps and rotors are nearly indestructable, but sometimes things happen. The cap part # is 000-158-52-02, dealer price is $179.00 while the rotor is # 000-158-40-31 and $40.50. FastLane has the rotor for $33 or so, but the cap is not available.
Don't get the aftermarket cap and rotor, you wont be happy with them and you'll only save about $80, insist on the Bosch parts.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.