You might already know about this, but just in case you don't. The oil tubes can cause a lack of oil to the cams which will result in a ticking sound. The MB dealer said that the tube have been upgraded. It is a simple DIY job that I my self plan on doing soon. Here is a great link to this fix. Tick, tick fixed tnx to Donnie!
How many miles do you have on your S420? They are a sweet ride.