Hi. I have a house from the 40's that I just got. I've been painting the place. I primed the kitchen with kilz 2, and I noticed that around a vent, the primer bubbled. I'm not sure what the previous owner used, but it looks like he sealed the vent on with some sort of caulk, or almost like rubber cement. Kilz 2 wanted nothing to do with that sealant. Any thoughts on what I should do? Stick some paintable caulk on top of that?