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A number of factors come into play here, most notably CYA. An engine's pistons can have valve reliefs to allow clearance but over time can collect carbon and become an interference engine. Advanced bearing wear coupled with high rpm could also allow collision in some circumstances. Head gaskets having been replaced and having the head machined adds to the brew. Subie wouldn't be the first to adapt a new stance on the subject, there are other OEs doing the same.
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ASE Certified Master Automotive Technician w/L1.
ASE Certified Master Medium/Heavy Truck Technician.
Certified EVT (Emergency Vehicle Technician)
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