Tammi,
"Bad" is not what I'm saying. Synthetic lube just doesn't get soft at as low temperature as the petroleum based lube does. That is why you don't want to use it in motors with wicks and grease pots. It doesn't wick into the bearings.
As for using T-F grease on plastic gears she doesn't say not to, just that some manufacturers say no lube and some say other types of Molykote lube and that one should be careful what you use on them.
I don't know what the white Singer grease is, but if it's what I've found on the plastic gears of unmolested Singer machines and it does look like it, then I'll start using it on my plastic geared machines.
redmadder,
I don't know if you've done anything wrong or not. But just in case I'd get one of those curved tip syringes and pump in some petroleum jelly.
Joe