if its the same as the Pajeros, they use a vacumm pump to lock the front hubs in when 4WD is engaged, think the "normal" concensus is that the pipes can come off or split or the vacuum pump/solenoid doesnt do its stuff, sorry cant be of much help as mine work and if it aint broke i dont go near it!!
and another reply.
Assuming the leve moves freely I would look at the solenoids on the D/S inner wing and all the hoses running from these.
HTH
Bill
