Some GM vehicles equipped with the 6.6L Duramax diesel engine were involved in a mid-year change. Some of the vehicles may have been built with a flywheel housing that uses two different style seals (left and right). This applies to 2010–2012 Chevy Express, 2011-2012 Chevy Silverado 2500HD/3500 Series, 2010-2012 GMC Savana and 2011-2012 GMC Sierra 2500HD/3500.
On affected vehicles that require seal replacement (if coolant is leaking out of the rear cover), the left (driver side) turbo tube seal is an orange O-ring (P/N 94056175) and the right seal is a blue/green press-in-place seal, P/N 12627895.
The machining of the flywheel housing for each style of seal is different and not cross-compatible. If the flywheel housing is removed for service, replace these seals.