Do any NM stag owners have quiet turbos? The ones i tested before buying all had the same noise, so I came to the conclusion that they're just noisy from factory (in a cool way) and it is not an indicator of imminent failure, as Brick is saying. They may often fail at around the 100k mark, but that's unrelated to the normal noise.
If it were my car and I couldn't find with 100% certainty what the oil was and when it was done (ie a receipt from a reputable business) then i'd just change it with a full synth 5W-40 or similar, and do the filter too. Oil colour is not a useful indicator of condition!
My guess is the turbo bearing lube issue occurs when the oil has been left in too long and sludges up. However, the failure could occur after an oil change as the detergents in the new oil start to clean up the mess.