Difficult to change the Diff Lock

Right pain in the arse given the recent snow, but I'm getting troubles with the diff lock. I can easily get high/low diff locked setting, but can't change back to non-diff lock without putting the steering lock on and giving it some welly (which following a large bang takes the diff lock off). Everything seems to 'crunch' into place - high/low, diff on/off etc; but just doesn't seem to want to take the diff lock off.

Any suggestions?

diff lock switch may be wound in too far ,it is operated by the dl selector and if switch is too far in it can jam selector ,dl selector is spring operated linkage may need adjusting so that it puts equal pressure on spring to put dl in and out,front out put bearing if worn can misalign diff and ioutput shaft dog teeth making operation more difficult