I took my car in for climate control work-see other thread if interested. I noted some oil leak, perhaps 1 qt in 1000. It was localized to timing chain covers. My mechanic suggested new timing chain rails since my car has 300k miles. I thought V8s had this prob but not the six. What is the answer? Also he rec replacing the timing chain while in there as the chain has 130K miles. Yes or no and why?

The oil leak is not a huge deal and is due in part because I changed from Castrol Synthetic Blend 20-50 to Mobil 1 10-30. Costco sells Mobil 1 for $3.50 qt.

Thanks for your knowledge/advice.