James,

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. http://www.peachparts.com/shopforum/showthread.php?threadid=37931&highlight=oil+tubes

How many miles do you have on your S420? They are a sweet ride.

Tom