Its an easy job to change the plugs on this model. Remove the air cleaner cross over tube, the the plastic cover over the plug wells. Plug wires should last forever if they are'nt abused, handle carefully. Clean out the plug wells with some sort of air blast so that sand etc. does'nt drop into the cylinder when the plug is removed. Use Bosch or Champion platinum type plugs as recommended. No need to change before 100K miles unless engine does not run good or fuel milage is down. RE wire attachment to front grill below fenders, could be to retain removable grill piece to access the tow rings. C280, 60K miles car is flawless.