Be glad you own a HeadShok, Maintainance on a these are very little. One thing that should be done at least twice a year is to inspect and lube the part under the boot.
First cut the top strip tie, take care as to not cut the boot, and pull down the boot. First check for contaminents around and on the steerer, if you find any check the strip tie seals for leaks, finding no leaks means you probably got a hole in the boot. To replace the boot you will have to tear the shock down, read the repair and dissassembly page for this information. If while riding or doing maintainance you find that the boot is torn it must be replaced IMEDIATELY.
After checking the area for grime and dirt, you can then clean out all the older grease. Then spray a coat of lubricant on the steerer for corrosion protection. Next a apply some greese to the exposed part of each slider (4 total flat areas the the bearings ride on). After the grease is applied move the shock in and out it's full lenght of travel to get the grease into the bearings. NOTE: if you find some surface rust on the steerer don't worry about it, if there is surface rust on the slides take fine sand paper (300 grit or higher) and sand the area (put grease on first then sand, once done sanding remove grease and reapply this keeps you from putting metal dust in the boot).
Also Cannondale recomends periodically checking the steerer for cracks, especially after a really hard hit. Check the steerer from top to bottom where it goes into the forks.