To get the tool box cover off, Turn the key lock a quarter turn counter-clockwise., it is a simple bar and lock-plate inside. The lock plate is welded to the cover , the bar on the key lock side gets in behind the lock place and draws the cover in on the right side.
The lock nut on the back side frequently loosens up, not enough to cause the cover to loosen but enough to make unlocking it the first time confusing. When the nut loosens the key lock will rotate all the way around.
You will find a place to put your fingers behind the cover near the top on the left side, Put your other hand at the bottom at about 7 o'clock, put your fingernails in back of the edge of the cover and wiggle out top and bottom back an forth and it will give way. Unlike the Air Filter and Electronic Box covers there is no hinge, it comes off completely.
Do not use petroleum based grease on the rubbers, in a year you wont have to worry about pulling the cover because the rubbers will be cracked and fall apart. Pick up some Silicone Based O_Ring lube. Pool stores carry it, Jacks 427 is a good one, there are others. Lube it generously. You can also rub a small amount of Silicone Grease on the plastic gasket surface on the cover where it rubs on the box sides.
-Q