It's always a good idea to seek a second opinion and don't just stick with the big dealers, there are lots of independent specialist mechanics who are often more tuned in to problems than dealers. More importantly they often cost less.

It's always a good idea to get a second opinion when facing the prospect of a large repair bill on something like an automatic transmission. Independent specialists who are working on automatic transmissions all the time often have greater knowledge about them than the dealership mechanics who don't work on them every day.

NOT really. The CLK430 is a great car and should give you years of motoring pleasure. The only thing to be aware of is that it is a couple of years older than your C-Class, but Benz quality is good enough and you shouldn't have any specific problems. The key is to keep up the servicing.