How about starting from basics. Do you know when was the last oil change and what type / viscosity was used. If not sure or even if you have the receipt from PO, I'd try good quality 5W-30 or 5W-40 and good quality oil filter.
Also, draining oil could give you some clues (hopefully no shavings or TC guide pieces)
You could also drop the oil pan at the same time and you'd be out cost of oil change and oil pan gasket.
Of course, if you find pieces in the pan, you wouldn't be changing oil just yet.

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