Bigfoot uses an Alkyd sealant, not Dicor for roof penetrations. Look for Plasticote white sealant in a quart can. Might have to go to a RV dealer, I can only find a gallon can on Amazon. Use blue painters masking tape to give you about an inch of the sealant on the roof and whatever it takes for the vent base.
I agree with others, you may be talking about the refrigerator vent. It will come off the housing. If you want to glue together I guess you could, but you should be able to buy just another vent. Krylon Fusion spray paint will pretty it up a bit after you work on it.