Mine was never that bad but I would certainly recommend changing cap and rotor arm.

Also, remove and clean the dust cover behind. I bought a new one and I think they are expensive - I shall find out today. The o-ring on the old one was very compressed so I feel better about the new one, although replacing it may have been overkill.

In that hot and hostile environment, I do recommend installing genuine MB-sourced parts as I've suffered with cheaper Bremi parts.

All the best.

RayH