I agree with you Leon, I don't think this is a lubrication issue but I think either there's some confusion as to what is really going on or she's got some play in the upper shaft or where the upper gear meshes behind the hand wheel.
To the OP - first, when you go to start sewing are you making sure the take up lever is at or just a hair over the top of its travel? On vintage machine this is the sweet spot for starting the machine as the previous stitch is finished but the new stitch hasn't quite started. You shouldn't have to help the machine get started if the take up lever is in this position.
My next suggestion would be to take out the motor and put it back in and see if the gears are meshing properly at the top.
Cari