Congrats, hopefully you'll get it soon.
If you plan on keeping your 300C for a long time then you might want to consider the extending warranty. I plan to get rid of the mine in like 2 more years. I've had mine since March 04' and have had some little mysterious problems on my ride that might later on turn into big problems. Maybe these problems might get bad right when the standard warranty is over. I'd hate to get stuck with a fat bill on a problem I've been having for a year and right when the warranty is over then the problem turns into a nightmare. I know from experience.
Don't mod the car if you want to have hassle free service from the service department and Chrysler. For example if you had a engine problem that will cost $800 dollars to fix and you've had an exhaust mod done to your car there is a good chance that DC will not cover it, if they do cover it, it might take a little arguing on your part to get it fixed for free. It all depends on the dealership and also if Chrysler is getting a lot of warranty fixes on 300's. If they are getting a lot of warranty claims on 300's, then they will tighten up the free fixes to people that only have bone stock 300's and then you'll be in a world of $h*t.
For example Mitsubishi is having a lot of problems with there Lancer Evolutions and a lot of owners are getting turned down for warranty fixes and the only mods they have are rims and things like that. If you read the fine print they can really screw you when it comes to warranties.
