Not familiar with Sympodium but I have owned several Wacom tablets. Prices of pens depend on the type of tablet. Currently use a Cintiq 24HD and the pens are available for about £60 on ebay.
More details of suitable pens are available on Wacom website.
My 2002 W220 has springs on both sides. Nearside spring broke a few weeks ago resulting in boot lid not lifting when unlocked.
Got a replacement from MB for a few £ and indy fitted it using a hook like tool and a lot of grunting!