There is a problem, that must be repaired, hopefully you do not have to replace the transmission, but more than likely it will take more than just a flush with new fluid. The conductor plate has electrical contacts and solenoids that control fluid pressure. Changing the conductor plate is a rather simple job. Will it fix your problem? At this point no one knows, because no testing has been done. Get the DTC codes read with a scan tool that can dig into the Mercedes codes. A general scan tool will not get you where you need to go. The scan tool must be programed to read a 2003/2004 Mercedes SLK 320 on a R170 frame. These NAG1/W (Chrysler designation) 722.6 (Mercedes designation) are precise pieces of machinery. The proper fluid is Pentosin or Shell ATF 3403 made to Mercedes spec's MB 236.10. Do not use Mopar ATF+4 fluid! There are several "clutches" in the transmission as well as the torque converter that are serviceable. Depending on labor it may be less expensive to buy a used transmission and simple replace the one you have. POINT is no one really knows what is wrong with your transmission. If you decide for a second opinion take the car to a transmission shop who are experienced with Mercedes/European transmission repair and start by getting the codes read. Good Luck.

PS. I may have made the mistake of assuming you have an automatic transmission! Most Crossfires are so equipped. If you have a standard manual shift transmission, some of what I have said is incorrect. However it will non the less be advisable to get a second opinion and learn what is actually wrong with your transmission. It may be repairable for less than a replacement.