Crankshaft rear main seal replacement involves removing the transmission and flywheel. Begin by removing the transmission, followed by the clutch pressure plate and disc for manual transmission vehicles, then remove the flywheel. Drain the engine oil and take out the seal carrier bolts from the oil pan, loosening all oil pan bolts. Carefully remove the seal carrier without damaging the oil pan gasket, checking for any damage afterward; if the gasket is damaged, replace it. A kit from BMW includes the rear main seal carrier and seal, along with a plastic support bushing for installation. Install the new seal carrier to the crankcase, ensuring to check for damage in the locating sleeves and bores, replace the gasket between the rear main seal carrier and crankcase, apply a thin coat of sealant to the oil pan gasket sealing surfaces, and lubricate the crankshaft seal contact surface. Use the plastic support bushing to guide the seal over the crankshaft, ensuring it is pushed on straight, then remove the bushing. Install and torque the seal carrier bolts to specifications, using new bolts at the base and coating the threads with sealing compound. Finally, install and tighten the oil pan bolts, then reassemble the flywheel, clutch or torque converter, and transmission, fill the engine with oil, and run the engine to check for leaks.