I think that rick_c s dead-on.
If the steering is 'drifting around' it's likley mechanical. It's a straight mechanical steerbox, so the play could also be in there.

If, by 'drifting around', you mean that the steering turns itself, then the problem is in the shuttle valve area. There are 2 springs that keep the valve centered. The valve is moved via the attacment to the drag-link. If a spring breaks, it all loosens up, and the steering goes wonky.