I have a low mileage 1995 C220. The plugs have never been changed. I am trying to remove the ceramic/plastic sparkplug boots. They don,t seem to want to pull off. There is a knob on the top of the boot to pull them with. I don't want to break them. Are there any special tricks to remove them. (WD40, twisting, etc.) Any suggestions. I did a search on other models but these seem differant.