Brian has it correct. 0000 or 000 Steel Wool dipped into linseed oiland lightly rubbed will clean off the grime and improve the finish without destroying the patina.
You should be able to get the 0000 steel wool at your local Home Depot.
A little bit of oil, lightly rubbed over several sessions will give a lot better finish than a lot of oil heavily rubbed in one session.
Be very carefull with the light rubbing. Too much/too heavy will remove the patina and the serial/inspection markings.
PAul