Outer Limits 4x4 Board

My full time 4wd 80 centre difflock is not engaging as it used to. It can up to take 5mins to engage and it disengages with a bang. Or I reverse to relieve the pressure to allow it to disengage. The gearbox is on the shed floor . I removed the difflock motor and engaged it by hand, it seemed to go in smoothly. I need to know if the problem is with the motor or in the transfer case. Any help would be appreciatde.

Have you checked the diff lock relay in the drivers footwell ? Also the wiring to difflock motor

I havent checked the relay, but with no load on the transfer, ie with 4 wheels in the air, it engages & disengages every time. You hear the relay click even if the diff lock does not engage