I don't think calibration is the problem. If the faulty meter showed a steady 2.1 ohms with probes shorted, then it could be calibration.
But since it starts at 25 ohms and drifts downward over time to near 0 ohms, that doesn't sound like calibration.
Fluke 289 has a minimum 10 year warranty. If you bought this new, you should have at least a 10 year warranty.