Most oil based lubricants won't help a heat riser, due to the heat in that area. The residue left behind when the oil burns away can gum things up. You might try some Never-Seez, which is made from atomized aluminum powder and very high temperature grease, or powdered graphite in a squeeze tube that is usually used to lubricate lock cylinders.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!