Non of the parts should AFAIK break down with normal use and PLA temp. but the parts made for countersunk screws might split
Regarding the Hot end nozzle mount, I do not like the original one, prefer a model with out the slots like this one:
RepRap Ormerod Extruder Nozzle Mount for cap screws:
[
www.thingiverse.com]
"...also the bracket that holds the z axis.."
If you mean the Z lower mount, chrishamm, the artist former known as Zombiepantslol made a version with conuntersunk screws:
[
forums.reprap.org]
..and if you mean the z-foot I think you would be much better of making one in aluminium or steel, make it a bit longer and mount it with two 6mm screws, should be obvious why, don't know why they did not do this from the start
Erik