No the back case is not Gold or gold plated, its bare stainless steel , which I thought was a bit ill suited to an engraved presentation watch. The bezel and lugs were gold filled and the broken lug appears to have been cast around a slender rod that was welded to the case. The only mark on the case at that point is a small round rough patch where the lug snapped off.
In looking the model up I found most did have a gold or gold plated back case.
A watch repairman I contacted who specializes in high end Omega and Rolex watches checked with Omega and was told the back case was no longer available.