I do know that on the M39 based wreckers there is a separate TM for the crane section. I was able to find that number in the early -10 for the M62.
If you can find that TM, there is good possibility that there is a detailed exploded view for that and most likely a repair procedure. If the innards are jujst a swivel, it should be just o-rings. If it is a pressure cylinder, which I doubt due to only a few small bolts, the seals can be sourced at any hydraulic shop, the o-rings should also be available there too.