I left the playfield rests bare after cleaning and they showed rust within a month.  I got them replated.  You shouldn't need to clear them after that.  The $35 minimum charge is pretty good.  Most down here have a $100 minimum.  There is also no point cleaning the existing parts before you take them unless you want to polish out any pitting.  If there is any pitting from rust it will show after they have been re-plated.  They acid dip to remove the contaminants and that gets rid of the rust and pretty much everything else.