The RH side will have to be removed to repair the differential lock, as the entire differential assembly must be removed and disassembled.
The clutch pins, #140, will be damaged on the ends from rubbing against the back of #110. The pins will have torn up the back surface and smeared metal across the holes of #110, where they have to enter to provide the differential lock feature.
With the pin tips damaged, #140 can not slide freely through #20.
The entire repair could be performed through the RH side with the RH axle housing removed.