Opened a few, Dewalt and Makita, when the hammer has had some **** in it and needed cleaning, they're not really all that complicated, just lay it out as you strip it somewhere clean
As Philip said, they're fairly simple. Be methodical & mark pieces for alignment with each other & the casing. The most complicated bit is the gearbox but you shouldn't need to dismantle it to check the hammer action, that is in the nose of the drill.
You may have to remove the chuck for access to it. Do that before splitting the case with the drill in low gear. Clamp the drill in a vice, remove the chuck locking screw (LH thread), clamp a large allen key in the chuck & hit it with a hammer anti clockwise looking at the chuck.
Probably a good idea to check everything, the puddle water might have got into the gearbox too!
