Have you fitted the Losi alloy diff supports in place of the stock plastic ones? Although the normal recommendation is that you don't heed to fit these until you've put a least a gallon through it I've fitted them to my 3 8T 1.0's from new and never had a problem with the rear diff binding or locking.
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Losi Eight T - Nova Rossi P21-7T- Hitec 5955's & Spektrum + TeknoRC Losi 8ET - Neu 1515-1Y - MGM 16025 & Hitec 5995's.
RC Heli's - Align T Rex 600 Nitro Sport - X-Cell Spectra G gasser.