Commercially available turbocharged internal combustion engines require robust system performance to maintain driveline power output capability. As in-service runtime increases, the accumulation of wear or deposits can adversely affect component performance levels. In a worst-case scenario, the component performance degradation leads to a vicious loop of declining system performance. Endurance testing of a heavy-duty diesel engine revealed performance deterioration over time. Oil deposits, resulting from oil mist associated with the closed crankcase ventilation loop, were observed on the turbocharger compressor and were tied to the deterioration. Cleaning of the compressor recovered initial performance for a short period of time. A different model of turbocharger, when substituted for the original, did not show the same degradation in output. This paper presents a study into the responsible mechanisms for performance deterioration and the compressor redesign that successfully avoided these issues. The results of numerical and physical investigations aimed at mitigating the system impact are discussed, starting with an overview of the observed engine and compressor performance decline, and an outline of potential areas of performance sensitivity to oil accumulation. Ultimately, the degradation of system performance was tied to the system response of deteriorating compressor characteristics. A compressor was redesigned and endurance tested to verify that the adjustment of engine-compressor matching and compressor characteristics results in improved robustness to oil-mist related performance degradation.