I have no idea if this is of any use to anyone, but I thought it was interesting.  Here’s a the link to download a 200+ government document that lists THE STANDARD NOMENCLATURE LIST of Spare Parts and Equipment as of January 1944 for GPW & MBs.  Sections of the document include: Maintenance Parts Procurement List (Section 2); Vehicular Spare Parts and Equipment List (Section 3); Organizational Spare Parts and Equipment List (Section 4); Ordnance Maintenance Unit Stockage List (Section 5); Depot Stockage List (Section 6); Geographical or Seasonal Maintenance Parts List (Section 7); and Indexes (Seciion 8).

Another document highlights the OPERATION AND MAINTENANCE OF GPWS & MBs from 1944.

I found this and some other documents related to GPWs, MBs,  M-38s and M-38A1s at Archive.org, a website that stores all kinds of information as a digital library and public resource (the site has movies, images, books, and more).  To find this information, do a search on Willys (or just click this link)

Here’s a couple images from the NOMENCLATURE LIST: