Driving it a lot and synthetic makes a big difference. Sludge builds up from cold running and stop/go driving at low rpms.

Eventually, the oil separator lines and vacuums line will fail from the constant engine heat. Your MPG will decrease rapidly, you will know when it happens, and then it will be time to remove the intake manifold and do some work.

Plan to do it in the spring when the weather is a bit nicer.