Joe, I guess my concern with the Vaseline is that it doesn't seem as thick as Singer motor lube, as you said. I would imagine a thicker lube would be less "runny", or more viscous, when it gets hot. I googled "vaseline singer motor lube" and the first result was this:
http://www.novamontgomery.com/singer...-the-month.htm
You have to scroll down quite a bit so I'll paste the excerpt here. She wrote (in Sept. 2012),
"
One other thing I want to mention – I have written a lot about lubricating your Featherweight motor with ONLY Singer lubricant. Remember the the horrors of the ‘repairman’ who contacted me and divulged that he was putting Vaseline in Singer motors? Within the past couple of months the first motor filled with Vaseline has come through my repair shop. The motor was not running – not even trying. It took quite a while, but the extreme “goo” from the melted Vaseline was successfully cleaned out of the motor. It is functioning just fine again! Please be cautious if you are told you must replace your motor. My experience has been that most of the time the motor can be cleaned and will operate as intended once again."
I'm not sure what to think.