After 7 years away I have just purchased a R171 and if any one wantes to help a returnee I woudl be very greatfuk to know where I can get an OEM one cheaply.
His - Denim Blue A220 AMG Line Premium / Hers - Obsidian Black R172 SLK55
They occasionally turn up on fleabay, but they're so darn useful that hardly anyone with an SLK parts with one, so your best bet is a dealer that you can persuade to offer a discount.