It's difficult to recommend anything with laptop hinges. They are a "friction hinge". Lubricating it with oil or WD-40 is NOT RECOMMENDED since this can produce a hinge that will no longer support the force produced by the weight of the display and housing, creating a display that won't stay open.
A little complicated but the best description I can find is this patent:
http://www.google.com/patents/US6467129
There are many suggestions all over the web, and there used to be a company offering "conditioner" for the old Titanium G4 hinges which used to seize up nicely and crack the display housing and laptop base.
The problem is that due to the contact area between the surfaces inside the hinge being almost inaccessible, getting an appropriate grease in there is near impossible by simple methods. This leads to the temptation to use a thin oil, but this reduces the friction beyond what is required to keep the screen in a balanced open position at a wide range of angles.
Of course, the cracking of the plastic mounts is most likely the result of the grease hardening or evaporating, which increases the force required to move it.
If you go ahead with any solution, resist the urge to turn the hinges whilst not mounted in place, as you can apply too much force by hand and break the mounting flanges of the hinge.
Superglue will often work to repair the plastics. I used to sometimes glue in place with superglue, then surround the cracked area with a two part epoxy to (hopefully) provide extra strength. All the usual cautions apply such as using a minimal amount of superglue (a needle as an applicator can help to allow a measured application), sufficient ventilation to prevent marking, and if you use the additional epoxy, make sure it doesn't interfere with the shape and fit of the hinge flange. Of course, you need to resolve the stiffened hinge or the crack will re-develop.
You'll end up in a Catch-22 where you need to work the hinge in place to free it up, but you risk breaking the repair to the plastic display housing.
Difficulty level - 10.
Good luck!
