I think it's better for SL to keep the O405s. The MK IV DM3500
is rather balanced already.
It would be more economical and efficient to bulk-maintain. No
point have 4 Lances in kjdep, 6 in wldep, the rest in amkdep. It's
madness if a "kjdep Lance" breaks down, because they probably won't
know what to do. 
Right now, if I want swap, I would gladly let AMDEP/BRAM swap their
Scanias to bndep for some MK IVs. Nice move that will benefit both
parties. (recent criticism about bn's MK IV, will amdep do
better?)
Swap O405s with bbdep is not good idea. bbdep no longer has
capabilities to effectively maintain the O405s. If you all are
thinking sl's O405s are too plentiful, won't amdep be worse by
number and percentage? 