unaccustomed to urethane primers, I (mistakenly) figured the sealer the instructions called for was only for making certain the primer didn't soak
up all the resin/gloss of the topcoat. reading further on a website of the paint (www.paintforcars.com) I see it's more for level bodywork.
(OK I was beginning to guess this on my own also)
I still don't know the "mechanism of reaction" for this.
Can anyone enlighten me on this?