Either will work fine. The 1N4007 is rated at a much higher PIV than the 1N4006 but is rated for the same forward current. I wouldn't assume that the original diode went bad because it's PIV rating was marginal for the application as the reason for the substitution of a "bigger" part. A lot of folks assume that whenever they find a problem and often end up substituting a part that causes even more catastrophic damage in the long run. I always assume that the original circuit was properly designed.
For instance, replacing a burned up collector load resistor in an amplifier with one with a higher power rating may only let that new resistor survive while other parts that are more expensive to go electron heaven because of another problem. Blown fuses and burned resistors are nearly always "secondary" failures, indicators of more serious problems with the circuit.
Dean