OER Parts offers a wide selection of Cooling System Components for your 1978 GMC C25. OER Parts offers 1978 GMC C25 Overflow System Components, 1978 GMC C25 Bottles and Caps, 1978 GMC C25 OE Style Radiator Overflow Jars, 1978 GMC C25 Stainless Steel Radiator Overflow Tank , 1978 GMC C25 Overflow Jar Bracket, 1978 GMC C25 OE Style Overflow Jar Cap, 1978 GMC C25 Billet Aluminum Overflow Jar Cap, and 1978 GMC C25 Radiator Overflow Bottle, Hose & Cap Set.