I've only used Seafoam for cleaning out engine oil galleries and only 90 to 120 miles before changing the oil. The previous owner never had his/her oil and filter changed at the recommended intervals, before selling it to the Abused Car Stealership which I bought it from in February, 2004. As a result, I'm still clearing the gunk out of the oil galleries more than 5 years later. However, as far as I can tell, all internal moving parts are getting proper lubrication, in spite of the gunk.