How do you replace valve stem seals on a T4?

To replace the valve stem seals on a T4 engine, first, remove the valve cover and spark plugs, then use a compression tester or air compressor to keep the valves closed. Next, remove the rocker arms and pushrods, followed by the cylinder head. Once the head is off, replace the old valve stem seals with new ones, ensuring they are properly seated, then reassemble the engine in reverse order, making sure to torque all bolts to the manufacturer's specifications.