well judging from the angle you have taken the pics from, none of the tracks of the PCB have been damaged, only the contacts seem to have taken some minor rusting.
Do NOT use WD-40 on this thing it will ruin it completely, WD-40 is used for lubrication and for removing rust on iron parts etc, NOT for PCBs. Use a proper silicon cleaner or a PCB Cleaning solvent which is available in the market. Advancer is an expensive item u could mess it up using WD-40
Secondly, it could be the problem to your rpm idling problem since the rust could prevent proper flow of current etc and could cause disruption.