Just a quick update. I took off the old mirror glass and noticed the heater element connections seemed loose. I disconnected the wires, cleaned up the connectors then connected it back up. I popped the glass back on and touch wood it appears to be working again!
Also the mirror I received from ebay was cr*p, the connectors for the heating element were far too small. So for anyone else with this issue, check the heating element connectors before buying new glass, and if you do buy new glass be careful which one you buy!