I have been asked where we cleaned our maxiclimber to try and remove its annoying squeak, this is what we did. Most people seem to have returned theirs but we wanted to try cleaning it first. Should you chose to do the same and it doesn't work or you cause damage, don't blame me!
See where the arrow is pointing:
We used a non scratch sponge pot cleaner and first of all used neat washing up liquid to scrub off said black marks. Then it was dried and using a soft cloth, rubbed the whole area from top to bottom with a light coating of WD40. This treatment was then repeated on the other pedal bar.
We found the squeak went away for about 2 weeks before reappearing, most annoying.
UPDATE FROM ORIGINAL POST: We now use just washing up liquid to clean away the marks, in the hope it might give less longterm damage than WD40.