Recently, while doing some other work on the Z axis in the printer, I found that one of the PTFE leveling screw blocks had failed- it was getting wobbly.  I decided to redesign the blocks for more stable mounting.

These blocks sit on the 4040 tee support frame and are held in place with an M4 screw and t-nut.  They are very stable and the thickness of the blocks matches the length of the threaded portion of the leveling screws.

Here's how they look mounted on the tee:

Their positions can be adjusted as needed just by loosening the M4 mounting screw and sliding the block along the t-slot it sits in.  

And a close-up showing one of the blocks installed:

More details and a link to the CAD file here.