Welcome to the forums! I purchased a 2005 LTD Roadster, not a SRT6, with 6K on the clock approximately three months ago. I haven't had any problems other than a screw in one tire. I have not experienced any of the issues you mention. My wipers continue to work just fine and there is no "whine" at any speed in my differential. My XFire idles so smoothly that I have to look at the tach to make sure it's still running. It amazes me how quiet this car is until you hit the gas. It also amazes me how you don't realize how fast your traveling until you check the speedometer. On the Interstate, I find myself traveling well above the limit without realizing it.

Three words: Quiet, smooth, fast...

Bob

P.S. averaging 24-26 mpg with mostly around town driving.