I use Mobil 1 in all my muscle cars and daily drivers and still change the oil about every 5 to 6 thousand miles and always use Napa gold filters, But they say you can go 10,000 but the oil looks pretty dirty at that point www.mobil1.com and its available at Walmart in 5 quart jugs
Noisey piston sound reduces as engine reaches temperature.
I researched this, and it seems to be fairly common on late 90's early 00's Subaru Foresters.
No loss if power, otherwise it runs fine.
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