Q: How to maintain and service Axle Shaft in a Buick Century and Regal?A: For standard differentials, it's advisable to use GL-5 hypoid-type gear oil such as SAE 80W or SAE 80W/90. However, for positraction/limited slip differentials, GM recommends a specialized lubricant designed explicitly for these units, typically available at Buick parts departments, due to the unique requirements of limited slip differentials with clutch packs. Regularly checking the oil level in the differential is crucial, ideally performed at each engine oil change or every 7,500 miles (12,000 km). Park the vehicle on a level surface, position a drain pan beneath the filler plug on the front of the differential carrier, and clean the plug and its surroundings. Remove the filler plug, and if the lubricant starts to flow out, the differential is adequately filled. If not, carefully insert a finger to ensure the oil level reaches the filler hole and add oil if necessary. Replace and snugly tighten the plug. When draining and refilling the rear axle lubricant, use a suitable gasket to seal the axle housing cover. There's no fixed interval for changing the rear axle lubricant, but it's recommended when purchasing a used vehicle or if it's been exposed to high water levels. Follow these steps: park on a level surface, set the parking brake, place a drain pan underneath, remove the filler plug, take off the axle cover, drain the fluid, clean the cover, seal both sides of a new gasket with sealant, reinstall the cover with a crisscross tightening pattern, refill the axle with the recommended fluid, replace and snugly tighten the filler plug, check for leaks after a short drive.