That is absolutely NOT normal and indicates either a break in the seal or a seal not properly installed. I would demand that both headlight assemblies be replaced. Eventually it will get worse and begin to damage components within the assemby itself. Of course, by then your CTS may be out of warranty and you will be stuck with the replacement cost which is probably why your dealer gave you the TSB B.S. I would also, if possible, find another dealer as yours is either ignorant or outright lying.
Also, high pressure car washes have been around for many years and will not dislodge lighting seals if they are properly installed in the first place. Were that the case, car mfgs. would be going broke replacing light assemblies up the wazoo!
Then again, they're already broke, so...
