Carlos - I have not used Toolbox in years. But I believe there are at least two ways to use it - one way saves off a single .sldprt file ("Create Parts" setting vs "Create Configurations"). A part file will be necessary for GC Workbench to deal with.
And you may want to put them in a Project labeled by Workbench as a Common Parts Library.
You could also try email@example.com, they are usually helpful.