Same here Before my Grand Cherokee I had a 91 full size Blazer
With the 350 T/b Used Valvoline synthetic for 15 year s and put on 195,000 hard miles on it and the oil always looked clean By the way I was washing the jeep today and was in my Garage and found an old quart of molbil 1 form a few years ago
Opened it up and smelled it and then smell the newer Mobil 1 and there is something going on here.
It is not the same thing
By The way Joe Let me know how you make out
This is something I need to follow up on
The vette has Valvoline and it looks good
but then I have not driven it much lately and has about 200 mile on the oil