Drobo 5n - Network Card Issues

I have a Drobo 5n that was working perfectly with the exception of very slow transfer speeds. After installing some network tools I could see that there were a lot of transmit errors. I changed the speed down to 100 full and got the same results but when I went to 100 half the errors stopped and the drive was usable.

However this is not ideal.

There appears to be something wrong with the network card. I have replaced many cables and tried on several switches including a cross over cable direct to a pc with the same results.

I have done firmware upgrades with no impact.

Looking to see if anyone has had a similar issue or any alternative advice. Could I even buy the motherboard out of warranty?