Actually I have D2 which is getting shorted. This is the second module I had to change because of this diode. I don't know what is happening as in the meanwhile the amp works fine but then it goes on protection and I find this diode shorted.
D2 has to charge a 10uf capacitor when the amp goes into over-current protection. There is a 4.7 ohm resistor that (I'm assuming) is there to limit the inrush current to the capacitor. Increasing the value of that resistor a bit (10-15 ohms) may protect the diode. It shouldn't affect the protection circuit but without thorough testing, there's no way to know if increasing the value would prevent the amp from going into protect quickly enough.
Another way to protect the diode would be to reduce the value of the 10uf capacitor.
Since this isn't a common problem, have you asked the manufacturer of the amp if they have any suggestions or experience with this type of failure?