Hello Stitch 1967,
Nice to see another member in Britain!
Here is the link to help you date your machine. The Y prefix lasted from 1920 to 1935.
http://www.singerco.com/support/mach.../single-letter
It looks as though you are doing a good job getting all the muck off. The machine should be a good runner. Is it a hand machine or a treadle?