Does anyone know if the rear main oil seal would fall under the 36,000 mile bumper to bumper warranty or the 5 yr/100,000 mile warranty? I have a 2010 GMC ...

Covered for 100,000 Miles/5 years*
Chevrolet will warrant each 2007 through 2011 model year Chevrolet passenger car, light-duty truck, crossover or van for 100,000 miles/160,000 kilometers or 5 years (whichever comes first; see dealer for details) with no deductible, from the original in-service date of the vehicle, for warrantable repairs that are required as a result of defects due to material and/or workmanship to the powertrain components as listed below:

Engine
Cylinder head, block, timing gears, timing chain, timing cover, oil pump/oil pump housing, OHC carriers valve covers, oil pan, seals, gaskets, turbocharger, supercharger and all internal lubricated parts as well as manifolds, flywheel, water pump, harmonic balancer and engine mount. Timing belts are covered until the first scheduled maintenance interval.

Engine: 2010 Chevrolet vehicles
All internally lubricated parts, engine oil cooling hoses, lines and radiators. Also included are all actuators and electrical components internal to the engine (i.e., Active Fuel Management Valve Lifter Oil Manifold, etc.), cylinder head, block, timing gears, timing chain, timing cover, oil pump/oil pump housing, OHC carriers, valve covers, oil pan, seals, gaskets, manifolds, flywheel, water pump, harmonic balancer, engine mount, starter motor, turbocharger and supercharger. Timing belts are covered until the first scheduled maintenance interval. Exclusions: Excluded from the powertrain coverage are sensors, wiring, connectors, engine radiator, coolant hoses, coolant and heater core. Coverage on the engine cooling system begins at the inlet to the water pump and ends with the thermostat housing and/or outlet that attaches to the return hose. Also excluded are the entire pressurized fuel system (in-tank fuel pump, pressure lines, fuel rail(s), regulator, injectors and return line) as well as the Engine/Powertrain Control Module and/or module programming.