it can be sometimes if you run into issues. to fix the plenum gasket you have to take the intake off because plenum gasket is on the bottom of the intake. the plenum gasket on all magnum engines usually need to be replaced after long enough time. they eventually start to leak. there are a couple theories why they start leaking there is one sure way to fix it.
here is a picture of the stock plenum pan with a blown gasket on it. you can ignore rust. intake came off a truck at the junkyard that had no throttle body.