How do I add my Custom Workflow Activity to FIM 2010 R2 SP1 installed on Windows 2012 server?

Hellos.

I have tried and failed to add my custom.dll into the Windows Server 2012  GAC.

We have a version of FIM 2010 R2 Sp1 running on Windows Server 2008 R2 and that was no problem. There seemed to be a gacutil.exe present on the system which added my assembly.

I cannot find gacutil.exe on the Windows 2012 Server.

I have downloaded and installed Windows SDK for Windows 8. However, when I try the gacutil.exe /i <myCustom.dll> nothing seems to happen.

Are there any guidelines how to add custom workflow activities to FIM when installed on a Windows Server 2012 system?

TIA

*HH