Burping a PSS Dripless Seal
The PSS web site mentions "If the boat sits idle for a long period of time (generally 3 months or more),it is necessary to move the carbon face back to allow a small amount of water to enter the boat. "
I could imagine an airlock happening if there's a high spot in the water feed loop - if the boat doesn't get going fast enough to cause a suction on the outside to pull the air out, and if the airlock keeps water from coming in.
Mine are plumbed in with a pretty straight line from the PSS to the raw water inlet on the engine, so any air in there should vent right out.
But it would certainly seem prudent to give it a pull after launching.