Outer Limits 4x4 Board

mentioned this on the members forum but as im sourcing lots of info i thought id bring it out in the open..
basicly its farked, but i duno why... wont engage when the wheels are on the ground under any load wat soever, the air just pours out the breather and the diff doesnt lock.. but if i jack up the back axle it will clunk in no worries, but then after about 30 seconds the compresser cuts back in, regains pressure, and cuts out, the diff remains locked, but theres a pissy little leak out the diff breather... anyone know whats needed to fix this??
how much work is involved and how much brass it will cost me? cheers!

Sounds like the rubber seal in the diff has worn out.
Not expensive to fix but a pain to do

speedy sleeves worn

O rings

cost fark all in materials but a bit if paying somebody to do the whole lot