Tammi,
It's not the PTFE that's the problem with the Tri-Flow grease. It's the synthetic base. The original grease gets soft and runny when it gets warm. Then it flows into the bearings. Tri-Flow grease doesn't get soft at the temps the motors reach, so it doesn't flow into the bearings, or through the wicks.
I have quite a few tubes of the old Singer Motor Lube accumulated. I'm gonna have to keep them aside for the motors.
Joe