Ditto. Inspection includes checking for damage or loose terminals, crusty terminal or tip corrosion (from arcing and ozone in the cap) and any dark dust in the cap interior. The dust is carbon from the rotor contact button, and as it wears, deposits a fine dust layer on the other parts. The sparks can use this dust to jump to the wrong terminal under certain circumstances and is called carbon tracking
. Note that you cannot clean the dust off, as it's nearly impossible to remove from the microscopic pores in the plastic, and carbon will remain to be an issue. If in doubt - change 'em out.