The actuator and shift fork for the LT95 diff lock are located in a housing that bolts onto the right-hand side of the front output housing. The right-hand exhaust runs just underneath this housing.
With the gearbox mountings removed, it was evident that the heat shield which protects the diff lock assembly was broken.
As I had a piece of aluminium sheet, I made a new heatshield by flattening the old one and tracing the outline.
Because the 110 is a permanent four wheel drive, there is a centre differential between the drives to the front and rear axles. If this wasn't the case, transmission wind-up would occur because of the variation in wheel speeds during cornering. By engaging the diff lock (actually it's a vacuum actuator), the vacuum from the engine moves a selector fork which effectively locks the front and rear propshafts together (the same result as depressing the yellow knob in a Series vehicle). It's not a get-out-of-mud-free card though; if opposite wheels are not getting traction, the vehicle won't move - even with the central diff lock engaged. This is known as being cross-axled, and unless each axle has its own diff lock you could well be stuck.
Here's a closer view of the vacuum actuator assembly before it was removed. It's no wonder the dashboard warning light did not come on when diff lock was engaged; the switch only had an earth wire connected!