2003 Volkswagen Passat Oil Sludge Affect Turbo??

I recently had to have my engine replaced on this car due to a known oil sludge problem. Thankfully, it was covered under a special extended warranty. When I drove out of the dealer's repair shop, the engine light came on. After a few days of diagnosis, I was told that the turbo had failed but it had nothing to do with the oil sludge problem in the engine. Everything I have read about turbos indicate that proper oil maintenance is required for proper function. I changed my oil religiously with synthetic oil. I am out $1500 for this turbo repair and would like to know if I have a case against VW or is it likely that the two problems are mutually exclusive??