I've found 20lb Xerox paper doesn't work as well. Thicker paper (30lb and heavier) works best if you want to use paper gaskets. Otherwise I've used RTV silicone with great results too. Ultra copper, ultra black, and high temp red all work. The stuff that's sensor safe should not contain acetic acid (vinegar) and won't cause any rust/corrosion while curing. If it smells like vinegar, don't use it.