These two accounts of the loss of GM 100 may be of interest.
1) Chapter 9 (End of a Task Force) in Bernard Fall's classic Street Without Joy. The chapter includes discussion of the GMs in general and the background/prelude to the final battle of GM 100.
2) An excellent article in Armor Journal (Jan-Feb 2001, pp 24-29) titled Death on the Highway: The Destruction of Groupement Mobile 100. Fall's book is cited as a primary source for this article. If you have AKO access you can find the back issue here:
http://www.benning.army.mil/Armor/ArmorMagazine/content/BackIssues.html
The article has been reprinted (with permission) online here:
http://a70thvets.com/file/Savage/G100/G100.htm
My impression is that while GM 100 did have M-24s previously, they weren't present during the battle in which the unit was effectively destroyed. M-8 armored cars and 105mm towed artillery were there.