Hey, all when I purchased my 03 E55 it came with the lower cooler at the base of the bumper. Guy said EC put it in. I have no plans on touching, but are there any maintenance tasks I need to plan ahead for? Is the plumbing simply in "series" with the rest of my cooling system. Any useful tidbits are appreciated.

If your supercharger circuit isn't split (no additional reservoirs anywhere) then the coolant for this will basically be in series as you thought, and no there is no real maintenance for it, ideally if you are modifying your E55 you are going to want to split this supercharger water circuit from the heated radiator circuit and add additional water volume to the supercharger circuit by either adding a 1:BMW Reservoir small and basically a fill point and will suffice for a basic split circuit OR 2: Water tank to replace your cabin filter OR 3: Trunk tank which will quite possibly need an additional water pump, all of which can be purchased online and through sponsors of this forum