We don't need to run
synthetic oil as we change
oil once a year, which is less than 3000 miles. I use
synthetic in my daily driver as I expect to get over 200,000 out of the engine. Bradd Penn realy sticks to the engine parts, when I remove the valve covers to adjust the valves everything is coated with
oil.
The cost from my local distributor, 10 miles from home, is $58 per case 15W40. No shipping charges. Comes to $4.84 per quart for real piece of mind.
As far as buying ZDDP, go to your local GM dealer. I think I paid $8.99 a bottle which is cheaper than ordering from Eastwood plus shipping.