I'm not telling, but suffice it to say I bought a new bottle the other week and used it today. My machine is now purring again. I had been oiling regularly, but my old oil was definitely "past its best", to put it politely, and can't have been reaching everywhere it needed to. So for the sake of the price of a small amount of fabric go and get some fresh sewing machine oil. Obviously this only applies to those of us whose machines need oiling ;-)
Lizzy