Hinge is suddenly quite stiff, and screen won’t stay closed

Your display lids hinge clutches are galling up from grit!

Follow this guide to get to the hinge areas MacBook Pro 13" Unibody Early 2011 Display Replacement Stop after Step4 and jump down to Step8 to full away the AirPort board to uncover the right side hinge (you don’t need to fully remove it) and finish removing the display carefully!

Now jump to this guide MacBook Pro Retina Display Teardown and to Step 3 as we need to carefully remove the clutch cover to gain access to the hinges. I use a chargeable spray can which holds 90% isopropyl alcohol to flush out the hinge area (making sure the area is at the lowest point so not to allow any wetness into the display). I then use a cotton swab (Q-Tip) dipped in WD40 which I have concentrated in the WD40 cans cap to wipe across the hinges, I often need to do this process twice to get all of the grit out using a pair of lineman pliers to hold the hinge twisting it back and forth.