Grove RT-60S, one outrigger does NOT go down

OK, so right at the end of this big job, something happened and one (right rear) outrigger leg would not go down.

It is a Grove RT-60S crane.

When I press "Extend" and that leg button, nothing happens at all, no oil comes out, no unusual sounds (not that it would be easy to hear with the engine running).

This same legs moves right and left without problems.

Would anyone have any relevant experience before I tear into it to fix? What is most likely to go wrong?

Thanks

Grove RT-60S, one outrigger does NOT go down