RepairPal Certified shops can diagnose and repair your 2002 Lexus GS300. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Part is about $100 if you DIY....otherwise, add labor too. http://www.lexussouthatlantaparts.com/products/gb/LEXUS/GS300/VALVE-ASSEMBLY--CAMSHAFT-TIMING-OIL-CONTROL/9914241/1533046011.html?partner=googlebase_adwords&kwd=&origin=pla