It is necessary.

There's a reason for this, and...

These days, hard-type rust-preventive oil is used, so it’s generally fine, but,

The head, exposed to the scorching summer sun.

The internal rust-preventive oil may dissolve and seep out from areas such as the back of the pressure plate.

As a countermeasure, caulking is required around the pressure-bearing plate and the cap.

Please use weather-resistant caulk.