Made a start today, as no work and no rain for a change !.
After striping the wheels, mudgaurds and hubs off: I heated the arm of the pressed in unit until it was glowing and the plastic/rubber internal bits were smoking well.
Then using a big hammer beat the arm outwards away from the trailer/ axle, the arm came out fairly easily. A bent bit of wire cleaned the last of the melted gunk out, leaving a clean bit of box to weld the mounting plate to.
Bits just ordered from Trailer tek who seem to do reasonable quality stuff at a better price than fleabay non brand.
HTH someone else in the future.