I've had sprinklers clogged by ants bringing in green material......

Hello,

Considering your extensive fountain experience and ruling out pump, tubing, and visible obstructions, it's likely that internal corrosion is affecting the water flow. Try using a vinegar solution to dissolve any mineral deposits. If the issue persists, professional cleaning or copper tube replacement may be necessary.

You need to revisit the pump. fountain pumps wear out and even if they are running and can push out water at zero head doesn't mean it is good. The impeller and and impeller shaft bushings will have an increase in tolerance due to degradation overtime and head pressure will be reduced.

Most fountain pumps for your application are under $20 so unless the statue has an enlarged prostate the pump would be the only problem if the tube isn't constricted.