Not the highest, but........
1998 Chevrolet Cavalier
334,000+ Miles
Original Engine/Trans
Engine History (Approximate)
1-8,000 miles - Unknown History
8,000-50,000 miles - M1 5w30 or Exxon Superflo Synthetic 5w30, whichever was on sale.
FYI - Exxon Superflo Synthetic used to come in a gold bottle back then. Conventional was in a red bottle.
50,000-315,000 miles - M1 5w30
315,000-Present - Pennzoil Platinum 5w30
OCIs were roughly 6,000, then tried a 15K interval or 2 with Extended Performance M1, then went to 5K intervals with M1, which I still do today, but wity PP every 5K.
Filter Usage
1-8,000 - Unknown
8,000 - 50,000 - Combination of AC Delco, M1 and P1
50,000 - 315,000 - P1
315,000 - Present - Mostly P1, sometimes Wix
Transmission History
1 - 50,000 miles - Stock Trans Fluid
50,000 miles - 100,000 miles - M1 ATF
100,000 miles - 315,000 miles - ST D/M or Mobil D/M (Had a slow fluid leak that I was slow to look at.)
320,000 miles - Present - Pennzoil High Mileage ATF