This isn't another Comet or MAX. The 767-300 was introduced 36 years ago and this example is 25 years old. If your running theory is that Delta's got an ETOPS maintenance program that's up to snuff for their own planes and other airlines, but somehow one plane is magically slipping through the cracks… well I call bullshit. If there were legitimate concerns the Ghanaian government would have raised them with the FAA or EASA. It's far more likely that Ghana wants a more prestigious plane than an old ratty 767 and this is the most pressure they could apply without raising the interest of foreign regulatory body.

  The history of aviation is littered with the crashes of airplanes brought down by problems that seemed to have gone away - see the De Haviland Comet, for example.

So what's the actual safety concern? The only specific issue called out was a fuel imbalance. You don't want to fly a long, ETOPS flight like that but it's almost certainly not an emergency. What were the other mechanical issues?

Airplanes can fly with all sorts of things missing or inoperative, and they do so every day. Safety issues are certainly one reason an airplane might return to the gate, but on a longer flight comfort and economic issues tend to become more important than they otherwise would. Autopilot acting up? You can fly the plane just fine, but not in the more precise RVSM corridors. Toilet clogged? Not a problem on a shorter flight, but on a long, full flight it might be easier to turn around (especially if Delta has a maintenance presence there). Bad weather at the destination?

With nothing but hand waving it feels a lot more like the sort of "safety concern" Al Baker would raise a stink about than an actual issue.