They are common for many failures, rear axle seals, engine coolant mixing with the transmission, burning engine oil which results on the driver running it low on oil and damaging/stretching the timing chains, GM just issued a re flash for the cam timing which keeps the ck engine light off...when actually the camshaft timing is off. My friends at he caddy dealer worn me not to rotate the engine back wards when removing torque converter bolts....aparently you can bend a valve.