What oil has been in the car for the longest?
Well... I ran Pennzoil Ultra 5w30 at times for near 6k miles. Other oils all less than that. For sure. Have cut down change intervals since 200k miles.
Long term running of any single oil...
Now probably a possible tie between Cam2 and Pennzoil Ultra..Have run a lot of Cam2 this past 2 years... Ran a lot of Pennzoil Ultra in the first 2 years. Castrol gold bottle is likely second behind those two.
I have run 30 different oils in the car. A lot of trying new and different oils in it.