Play in the turbo's shaft will eventually allow enough oil into the exhaust flow to create blue smoke. Any hint of blue haze from the exhaust when driving indicates the CHRA will need replacing. The turbo compressor runs around 250K rpm so the shaft floats on an oil film. There's clearly a small gap between shaft, bearings and seals, but when that gets palpable, it means there's some wear. However, I wouldn't rush to buy a new CHRA unless there's a faint blue emission. Lack of clean oil in the sump kills turbochargers.
TC
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