For the THIRD time, one of our (2) Grohe Freehanders arm is not able to move. The first two ended up broken and needing replacement (we had tried to loosen and/or tighten the allen screw behind the arm to no avail). Now, the same problem has happened again (on the 2nd fixture). Is this a standard problem from putting water through a moving part? Is there any fix? We don't want to touch the thing because we don't want to break it, but we can't move it either up or down!

SOURCE: i have agrohe shower fixture with poor pressure

If the shower head is clogged (even if it it is not I would still do this)
remove the head and soak in coke (yes, it works), CLR, vinegar or bleach and see if you can dissolve the debris. If that is not the culprit, check to see if there is access to a shut-off valve behind or below the shower. It will be inside of the wall and is only acessable through a hole in the wall.

If that is not the case, it is now time to consider replacing the shower body. This is an involved job but something very doable by a competent homeowner.

Hope this helped.

SOURCE: leak where Grohe shower head attached to the threaded pipe

using a pair of vice grips wrapped in a soft towel( to prevent scractching) turn the shower head in a counter clockwise direction to remove it then apply liquid teflon (real-tuf) to the threads on the shower arm and tighten the shower head but dont over tighten it liquid teflon is more effective at sealing leaks than teflon tape and it can be wiped clean