Beautiful_Sound,
Every Singer I've had apart that still had it's factory plastic gears in it, were greased. Most had some sort of white grease on them and a couple had some yellowish grease. I don't "think" it was lithium grease.
Singer sells a white grease in the little blue tube for plastic gears, that's what I'd suggest you look for if you don't want to order in the Tri-Flow grease.
Joe