Muky was made by Induguay S.A. "Fabrica de Juguetes Muky" (in Spanish: "Muky Toy Factory"). Established by the DeConti brothers, the company was located in the city of Gualeguay, Entre Rios province, 145 miles north of Buenos Aires (Frasinetti No date).
Virtually all of the models made by Muky were copies of early Mattel Hot Wheels like the Custom Corvette, the Lola T70, the Custom Eldorado, or the Dodge Deora. Thus the company is often called the "Hot Wheels of Argentina" (Weber and Sahakangas website). Muky were not as popular, or as collectible today, as the country's Buby toys, which made Argentine Ramblers and Falcons and other vehicles that may have been more familiar to children there (Sinclair 1976).
Change of Management
In the late 1970s, because of the worsening economic environment in Argentina, the DeConti brothers moved to Brazil and began manufacturing toys there called Super veloz. In 1984 or 1985, a certain Dell Arciprete bought Muky, and using most of the same dies, again began making Mukys (Frasinetti No date). Arciprete's Muky also added a few new vehicles. The Arciprete family ran a fumigation business at the same time as Muky (Frasinetti No date).
The later Mukys were numbered from eight to 40, numbers one through eight having been lost along the line somewhere. Also, these later models' chassis were cast in plastic and Mukys were distributed to Uruguay and Spain, besides the patria Argentina (Frasinetti No date).
Questions on Tooling
How Induguay came to possess the Mattel dies is uncertain; one story is that the DeConti brothers stole the dies from Mattel, but two other prevalent theories exist, both logical. One is that the models were carefully copied from blueprints (Frasinetti 2009; Frasinette No date). Another is that third party agents, with the approval of Mattel, sold some dies to the De Contis (Frasinetti 2009). In any event, perusal of catalogs of old and new models shows that few of the 37 models originally manufactured by Induguay were ever reissued by Mattel. Apparently, the Arciprete family has kept the tooling and doesn't deny that they might again someday make more Mukys (Frasinetti No date).
Frasinetti, Bob. No date. Muky, Made in Argentina. Joe's Diecast Shak webpage. 
Frasinetti, Bob. 2009. Muky diecast made in Argentina. Website. 
R. F. Levine. 2009. David Sinclair in the Driver's Seat. Lake Erie LifeStyle, web published December 1. 
Sinclair's Auto Miniatures, Inc. 1976. Typewritten Newsletter and sales flyer. 12 pp. Erie, Pennsylvania.
Weber, Dave, and Kimmo Sahakangas. 2003. MUKY of Argentina. Website sponsored by Toy Collector. August. 
(Note: Dave Sinclair is a well-known collector and vendor of diecast and other automobilia. He started selling diecast vehicles in 1964. Sinclair nearly single-handedly brought specialty European diecast to the U.S. during the 1970s. Information from his newsletters and catalogs is respected period information on the subject (see Levine 2009.)