interchangability

Hi Everyone A colleague of mine is about to ditch his Audi (hoorah) for a 2009 CLK 220, he wants to remove the Audio 20 standard fit head unit and replace with a Sat Nav version. Is there any particular unit he should/shouldn't be looking for, is an interchange possible? He's looking at...

My S124 E200 has developed an exhaust blow; obviously the manifold isn't going to be the same as on 6 cylinder models, but how much of the rest of the system is the same as on other 124 models? I only ask because there's been a few 124s going cheap or breaking recently, and as my car isn't...