Hey Gizzer...I use Peek metal polish for them. I don't know what these cars normally collect around this particular orifice so I'm not sure if what I do helps or not, but it keeps the stainless nice.
Did you ever get any sill guards btw?
Your neighbour.
Howdy neighbour
Looks like I need the same polish as you to match your shiny pipes (ooer!)
Haven't got the sill guards yet - will give you a shout when I actually get around to it.