Before tearing into valve stem seals check the intake manifold for Oil inside, check the crankcase ventilation hose where it plugs into the front of the intake manifold. If they are wet with oil that is most likely your oil and smoke issue. True valve stem seal failures smoke on start up and quickly clear up while running. If you have an air leak in the engine it will suck oil into the intake manifold and cause the smoke at idle problem many report. Many items can leak air into the engine. If you have an oil leak externally you know air can also leak internally at that point of oil leak. Common leak is the valve cover gaskets, oil filler cap etc. Seal the engine before changing valve stem seals. My 2008 4.8L X5 was a smoker 35,000 miles ago, does not smoke today. OEM valve stem seals still in it. Original problem was at 100,000 miles, now at 135,000. Just food for thought. We also fixed my son's 4.4L X5 same way, no valve stem seals. Test is pretty simple, check for oil inside the intake manifold, there should be zero oil there if the engine vent system is working proper. Valve stem seals can fail but they have unique smoke issues when they fail. When you replace all the gaskets, Orings etc as you change valve stem seals you will also re seal the engine. How do you know at that point which issue caused your smoke. There is a ton a labor involved in sealing one of these engines so I understand if you are paying a shop to do this, change the valve stem seals while you are doing the job since the valve covers are off. If you do the work yourself you might measure the need for valve stem seals differently. There is no way for valve stem seals to put oil in the intake manifold so if you find oil in your intake manifold you most likely found the oil use issue on your engine.