cleaning valve covers

[SVXMAN2001]

I searched Chike's post on how he cleaned his valve covers by using grease lightning with positive results however may be harmful to aluminum. I used a rather generic engine degreaser on my valve covers and there are still stains on it, most of the grime is off but i want these babies looking like new! Is that possible or am i just expecting too much. ARe there other products out there better than grease lightning? Also is it ok to use steel wool to try and get the stains off? thanks, chris