"...a simple back plunger" weight wiring controls power money.
"...a front screen on the scoop" err, the screen on the ovens is causing one of the problems, and the scoop is not equipped with "shakers" to deal with it. [I know I know add shaker motors to scoop too...]

"How about coating the scoop with Teflon?" Adding a soft material containing carbon and fluorine to your chemistry sample collection equipment is probably not a good idea.

I believe that they thought of and counteracted quite a few possible glitches in ingenious ways. I also believe that the mission a) is already quite successful, and b) within a few months will be seen as wildly successful.

You know, this public handwringing is one of only two good reasons I can think of why NASA should be less forthcoming about the activities of ongoing missions.