This is a common problem with the Traxxas Pro 15 engine. As the engine gets older the starter shaft and the starter shaft bushing in the back plate wear and allow oil and fuel residue from the engine to contaminate the one way bearing causing it to slip. Replacing the shaft, back plate-bushing assy. and the one way bearing is the only way to fix it properly. If your engine has 3-5 gallons of fuel through it I would take advantage of their excellent engine exchange program and get a brand new engine. In a few months the new TRX 2.5 (.15 cubic inch) engine will also be available through the engine exchange program. And yes there is no problem using a starter box to start the Nitro Rustler.