...all of these caps last for many decades without measurable deterioration...
The results are this mic has never been quieter.
1. Properly working U67 power supply filter capacitors will detrimentally alter the sound of the mic?
2. Changing parts on a collectible item will affect its value, even if that change will restore functionality?
3. Listeners will not mind hum in a recording created with a defective power supply?
4. Something entirely different?
If you cover the outside of an electric guitar with aluminum foil, that will affect the resonance of the instrument, ... A properly screened Stratocaster is done inside the instrument. ...
The U-67 power supply was repaired. Repaired because the original caps had failed. This is not uncommon on 40+ year old designs.