Changed the spark plugs today to have the updated NGK version that ends with a B. First time doing this and was surprised how incredibly easy it was. Was also surprised to find oil in the spark plug threads. Wasn't in the spark plug itself but just on the threads on all plugs. Gaskets?
Yep, valve cover gaskets are known / common to leak / seep. Those valve cover gaskets are horrible. Tightness / torque has to be perfect and remain perfect. If torqued too tight or too light oil will leak or seep. Check the valve cover gasket bolts regularly and ensure they are torqued to spec.