1. Unless it is a Crossfire specific part, you will have better luck ( and less $$$ ) getting the same part for a 2003 MB SLK320.
2. The rear window bond issue is common to ALL roadsters, regardless of location. There are 2 contributing factors :
a. Heat.
b. driving with the top up and the windows down ( wind buffeting )

To factor into the cost, a new top is @ $1200, you can replace it yourself ( I did a DIY on that ), or pay a shop $500 - $700 to do it for you.

Good luck, Rose !