Depends what the problem is:
If it's simply a stiff/seized wind speed bearing then the mechanical part can be replaced.
But if it's a circuit-related issue, eg reed switch in an old Vue going faulty then chances are that the best solution will be a complete new ISS (or a Davis refurb which is close to the same thing other than the case).
Vue stations up to Rev F (can't remember exactly what year this maps to but eg 2011/12) did have separate sensor and transmitter boards which were individually replaceable, except: (i) this was later superseded by an all-in-one harness for improved reliability; and (ii) it's getting increasingly difficult to source the individual spares for Rev F and before.
All in all for a Vue dating from eg 2009-2012 IMO it's best to replace the complete ISS. The original Vue sensors will have given decent service for eg 8-10 years but will all be wearing and drifting. And the cost of the replacing individual parts, especially the transmitter board, is still not cheap and may require other parts being replaced before too long. Best to bite the bullet and replace the complete ISS.