I would use a product like "KROIL" or "PB Blaster" and almost NO force... Just time.
Kroil =
http://www.kanolabs.com/
PB Blaster =
http://www.blastergroup.com.au/index.html
Soft Brass bristle brush and these two have always worked for me
I now HAVE to have a machine with the cross ways hand crank... have to..... sigh...