Are you fixing it or are you making the inevitable failure even more dangerous? The answer is not easily determined.
The current solution is to drain the reservoir of water as fast as possible--this removes pressure on the hillside, and reduces the scope for damage should the thing actually go.
As for actually patching it, the solution is dumping lots of grout. But that only helps if the slope is actually stable and capable of supporting the embankment and dam. If the slope is washing away, all of your patching is just adding more weight to a structure that can't support its own weight anymore.
Now this guy was a great salesman. It leads you to wonder if his apparently high success ratio was a result of pure luck, if there's some truth to his "evaporative mix," or as suggested in the article, he had great meteorological prediction skills.
If weather patterns are not independent one year to the next, then just the fact that only statistically significant drought-ridden cities call for his help probably suggests that all of these cities are "due" for rain regardless.
The current solution is to drain the reservoir of water as fast as possible--this removes pressure on the hillside, and reduces the scope for damage should the thing actually go.
As for actually patching it, the solution is dumping lots of grout. But that only helps if the slope is actually stable and capable of supporting the embankment and dam. If the slope is washing away, all of your patching is just adding more weight to a structure that can't support its own weight anymore.
While looking at old examples of dam failures, I came across https://en.wikipedia.org/wiki/Sweetwater_Dam#1916_failure ... this seems awfully similar to what's happening at Oroville right now.