i have an 05 (50000KM) and the diff howls pretty bad. A lot of people on this site have the same problem. Other than that i love my cts.
Most of the Buicks of that gen are bulletproof. A friend just recently got rid of his supercharged regal, had over 240,000 miles. The best thing he ever did for that car was get rid of the stock 7 degrees of KR right from the factory. A tune and breathing mods netted him a low 14 1/4 and about 5 mpg better. Great cars only let down by so-so interiors are strong but somewhat overwhelmed trans. He was making 310 whp+ for the last 90,000 miles, too.Biggest problem with CTS is that you will love it; very reliable, quick, safe, etc.
It will not have the ride of the LeSabre, but life is tough. BTW, your LeSabre will give you about 200,000 miles. No built in problems with those cars. (America'a best kept secret; keep it for a child or grand child.)