The Buick 3800 engine is a large, high output V6 engine. The oil pump O-ring is located where the oil filter connects to the oil pump. The oil inside the oil pan must be drained and the oil filter removed to replace the O-ring. The replacement O-ring must be specific to the 3800 V6 engine; you can purchase the O-ring at an auto parts store.
Raise the front of the Buick using the jack, and support the front of the Buick on two jack stands. Get under the engine and position the drain pan under the drain plug on the bottom of the oil pan.
Remove the plug from the bottom of the oil pan using the socket and ratchet. Drain the oil into the pan, then replace the plug to the oil pan.
Twist the oil filter in a counterclockwise motion until the filter comes off the oil pump. Using the flat head screwdriver, pry the O-ring from the oil pump and pull the ring off the pump.
Place the new O-ring in the same place as the old one, and push the ring into place. Replace the oil filter to the bottom of the pump, and tighten the filter until it is snug.
Remove the drain pan from under the Buick. Raise the front of the Buick using the jack, and remove the jack stands. Lower the Buick to the ground.
