“QSC” Aftercooler O-Ring Kit
(Early Aftercoolers use 3 O-Rings, Later styles use 4 O-Rings)
Cummins P/N: 3971678, 5312664 
Cummins P/N: 3974192 (3pc set) Retail $369.23 per kit
Kit includes stainless tube o-rings