Always clean off any dirt, grime, or chemicals promptly.
A lot of dust and grime gets accumulated in these areas between string changes.
Be sure the chain you are using is free from grease or grime.
Some grime can be poisonous to your eye, and catching an insect on your pupil can lead to severe pain that will immediately take you out of the race.
Years of accumulated grime had to be removed, probably built up over the life of the box in London.