Synthetic is a great cleaner. It causes all kinds of problems with refrigeration units too.
If there was anything coating the inside of the engine it would have been cleaned off and run through the system. If the filter got plugged early it would bypass all that junk through the engine.
I would guess that it was not all that clean to begin with and using synthetic signed it's death certificate.
If you get it good and clean go ahead and use synthetic, but I don't like it so much. Remmember it is good for starting crankcase fires too.
