MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
Ok, I understand!
The "Print Cooler" it is not intended as belonging to the "core" of Dondolo, (the X-Carriage itself is on the "borderline"!).
Among the Dondolo files the PP4 is named "Extruder_Chain_Support_v2.stl" and is slightly different.
The PP4 part referred in the "Assembly Guide" (and the X_Carriage) is uploaded in the project:http://www.thingiverse.com/thing:1017953 (Prusa i3 Hephestos Dondolo Upgrade Kit.
I hope this will help you.