Hi Sharron, sorry I can't help with any local recommendations as I'm not in your neck of the woods, but I can offer some basic advice.

Firstly I personally wouldn't go to a Mercedes dealer despite the car being basically Merc mechanicals, unless you are very wealthy, and going to an MB dealer doesn't neccessarily mean a better job either, just a bigger bill,I've owned a Merc E class and like most owners I used a Mercedes independent specialist instead.

The key thing with the Crossfire is to make sure they use a genuine oil filter and the correct oil, I take mine to a local 'all makes' garage who I know and trust.

I would do a Google search for a Mercedes independent garage nearby and see what comes up, they will have the knowledge to ensure the correct oil is used, and the correct procedures are followed, they will have experience of SLK320's (which is basically what we have)

It isn't a majorly complex car but it isn't one I'd take to a garage without experience of servicing them.

Hope this helps

Edit - just checked on a couple of Mercedes owners forums and www.threepointsltd.co.uk seem to get good feedback