johnlee -- A hot pressure wash would be good or take it to a car wash and use the soap then water. You can start with engine degreaser but it will leave a film that will need to be removed. I'd recommend following that with an automotive type wax and grease remover or "precleaner" before and after sanding. Before sanding to remove any surface oil that pressure washing may have missed and after to remove fingerprints to avoid "fish eyes". Finish sand to 320 or 400 grit. Use a self etching primer on any bare metal before painting. You can get it in a spray can at an automotive paint store where you get the precleaner. Both also available online.
self etching primer https://www.autobodytoolmart.com/dupli-color-aerosol-self-etching-primer-dpp101-p-12713.aspx
pre cleaner https://www.autobodytoolmart.com/klean-strip-prep-all-wax-grease-remover-gsw362-p-14855.aspx
I managed a body shop about 16 years. Painter for four. Any more questions shoot me with a PM.
self etching primer https://www.autobodytoolmart.com/dupli-color-aerosol-self-etching-primer-dpp101-p-12713.aspx
pre cleaner https://www.autobodytoolmart.com/klean-strip-prep-all-wax-grease-remover-gsw362-p-14855.aspx
I managed a body shop about 16 years. Painter for four. Any more questions shoot me with a PM.