There is no way I would ruin a car by cutting a hole in it for spark plug access. I would rather pull the engine and change the plugs this way than trash that sheet metal in a structural area.
Man,I ruined this thing a long time ago. I cut, hack and drill as I see fit for the task at hand. This task will aid in regular maintenance, and will be well worth the sheet metal removed. I will be plugging the hole with a metal plug to prevent road grime from entering the engine bay.
I appreciate your point of view though, if I wanted to retain full value of the car I would not cut or drill the factory sheet metal.
