The gears need grease because the oil flings off of them leaving them unprotected. The general rule for anything high speed rotating or reciprocating - is oil every 8 hours. The gears though, I think would need it sooner than that because of the cross cut gears meshing together and squishing things out. My 201HC is greased (as is my potted motored one) and all I can hear when I crank is the hand crank.
From what you're saying then Tri-Flow isn't a direct comparison for Finish line then. On the TF bottle at least, there's no mention of synthetic.
Right. 2 other vendors are selling their own formula for grease and state that you shouldn't ever use PJ.
Sew-Classic doesn't sell her own brand and on the link I posted above that links to her Tri-flow grease page - it states that you should not use TF Grease in the motors, only PJ.