I live in Québec Canada. My 1997OBW showed this problem one month after I bought it new 11/29/1996. I complained during four years while the piston slap increased and when a knocking sound could be heard two years later. The mechanic told me that when the timing belt would be change the knocking sound would disappear, but it did not.
The Subaru dealer manage to have the short block replaced à 128,00Km free of charge and labor. I never heard a piston slap since and my OBW has now
207,000Km. and running perfectly. Best of luck to you.
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