On my Satas and Finex there is a gasket in the cap assy.
I don't like leaving any soft parts (not metal) in cleaner very long.
The aircaps on my Satas and Finex get cleaned first. They won't sit in the solvent cup over a minute tops. No real need to sit longer anyway.
I clean all of my guns immediately after use so it doesn't take 5 minutes to completely tear it down (minus the air valve and fan assy), clean, and reassemble.