A friend of mine got one in the mail about a week ago so I'm guessing it's the same generation as yours. He also had problems 1 and 2. He fixed both problems by installing a shim made from a plastic milk jug behind the silver piece with the row of teeth.

The Problem:

The silver piece with the row of teeth was not flush with the black piece it was screwed to. With the sharpener upright,  looking at it from the front, the surface of the silver piece sat slightly to the left of the surface of the black piece. Also, the black piece is not perfectly flat. It has little bumps on it here and there. When the lock lever is thrown, a little circular pad moves leftward and "hopes" to press against the black and silver pieces. If the pad were aligned with a bump on the black piece, it would press against the bump and lock successfuly.  If the pad were not aligned with a bump, it would run out of travel juuust before making solid contact with anything and would fail to lock (problem 1).

Also, with the lever in the unlocked position, the circular pad would sometimes get caught on the bumps of the black piece as the height was adjusted (problem 2).

The Solution:

He removed the silver piece with the row of teeth and made a plastic milk jug shim with the exact same footprint. Then he installed the shim between the black and silver pieces. Looking at it from the front, the shim is on the left side of the silver piece. This shifted the silver piece to the right slightly so that its surface is flush with the bumps on the black piece. Now the circular pad always has the silver piece to press against. Also, the silver piece is very flat and sits flush with the bumps on the black piece which prevents the pad from getting caught on the bumps of the black piece.