broken valve spring

Looking for help here. Have a dealer playing Parts Darts and lying to my face (or are ignorant). 2010 Genesis 4.6 with 92,000 miles. I've owned it since ~50k miles and it's been extremely reliable. Only repairs being battery replacement (~70k miles), and Alternator replacement (~80k miles)...

My 2009 Genesis has the 4.6 V-8 with 86,000 miles. A couple of weeks ago it just started running very rough (missing) but with no obvious cause or noise. Limped it to the dealership, where it has been for almost two weeks. First they said it was a computer problem but that did not fix it...