Where did the new gasket come from? I see some vendors have two styles, original foam and molded rubber.
I don't think vaseline will do anything to soften the rubber.
Let us know how your efforts go.
Thank you sir; it's a Precision brand gasket definitely molded rubber. It fits the channel perfectly. I agree re: the Vaseline option. Tonight after work I'll pull the vent again and chamfer the outer top edges of that gasket - I bet that will solve it. Will report back.