The only product with a reputation of working is http://www.auto-rx.com/ (Auto-RX). Don’t bother with synthetic oil. Follow the directions of Auto-RX to a tee.
The engine will not likely have a long life but is not likely junk either. No one can say. Most engines last at least 300k with regular oil changes. Maybe you reduced it to 100k-150k.
Good luck.
Most likely the engines’ life has been greatly reduced.
This is what a BMW engine looks like after 60k miles of no oil/filter changes:
Thanks for the detailed reply. No doubt you’re aware that it’s not the length of the dipstick (who hasn’t said THAT?), but the distance between the top of the stick and the markings that’s important.
“Keep in mind that lubrication is all by gear tooth splash” – Yeah, that’s how I pictured it.