Outer Limits 4x4 Board

Interested in fitting an Auto Diff Locker to the rear of the old MK SWB, currently a standard diff. Had a quick search but nothing specific.
Second hand if available around Sydney.
Any ideas as to pros and cons in first sourcing one and then fitting up appreciated.
Anybody had any problems with them, fitting, not working as expected, or maintenance, specific oil etc.

Thanks