How to Lubricate a Hammer/Rotary Drill
Here's the relevant bit, which includes some liability tone:


  Your tool was properly lubricated before leaving the factory. In from two to six months, depending
  upon use, take or send your tool to an authorized service center for a complete cleaning, inspection
  and lubrication. Tools used constantly on production jobs will need relubrication more often. Also,
  tools “out of service” for long periods should be relubricated before being put back to work.


The simple fact is that it doesn't need periodic lubrication for the casual user. It would be different if you were a professional drilling dozens of holes every day. 

If you like, dab a little common grease in the chuck on occasion. There's a lot of slop (movement) in that type of chuck, and friction can heat things up if it's totally dry.