This is my 67 year old Mother's car. She's had it since 1996 and it's gotten fair care over the years, but has developed a valve train tap on the passenger's side which comes and goes. This car has hydraulic lash adjusters unlike later models. I put a pint of Marvel Mystery Oil in the crankcase about a week before doing an oil change and adding the Auto-RX. I cut open the dealer installed Subaru oil filter to see what was in there. If I can I'll post how many miles that filter was in service, but the records aren't here with me at the moment. I installed a Purolator Classic oil filter along with Chevron 10W30 and the Auto-RX. I'll change the filter between 1,000 and 1,500 miles to see what we're getting with the Auto-RX. This is just another case study so take it for what it's worth.