It *might* be as simple as just removing a shim or two to solve the problem.

If I remember right, yours has a Railko bush on the top and
a taper-roller on the bottom. If the play is at the top, then
it could be the upper pin - the Railko swivel pin is inclined
to wear a bit (it usually goes a tad oval), but often before
this the thrust washer (a disc of some interesting material)
that sits under it in the bush is likely to, er, dissapear (as
in get turned into an oily mush). Taking out a shim will
compensate, probably for quite a while, but really the pin
needs to come out, be inspected, and a new thrust washer put in.
You can actually do that with the hub in place, but it is heavy!
The upper pin housing is surprising robust, but does need to
be checked - you can see in it with the upper pin removed.

If the play is at the bottom, then the roller bearing could be,
in trouble - but beware, the lower swivel pin relies on the upper
being tight - any major slack in the upper pin can make the lower
one look knackerd, though usually you'd get oil leaking through
the swivel ball oil seal as well. Inspecting the lower
bearing without stripping the whole assembly is not easy,
but usually only fail when the swivel is being lubricated with
water/mud rather than nice clean oil.

Richard