The gold ring round the centre you're talking about is the clamp ring that joins the exhaust housing onto the centre (turbine wheel).

VF series do not have seal rings at this joint like the Mitsubishi ones had, they have (ceramic i think??) seals behind each wheel either end of the shaft. You can't really see them (there is a metal shroud on top) and you would need to remove the wheel/s to replace.

I assume the shop didn't rebuild the cartridge?

About the only thing I can think of if the centre cartridge actually is leaking is the seal under the wheel (cartridge rebuild time).

A VF39 is a journal bearing turbo, so the cartridge can be replaced/rebuilt, but is it economical if you can pick up a good ball bearing turbo cheap...choices time. And don't get me wrong the 39 is a good turbo, I'm using one on a basically stock 2.0 V3 engine and it got me a 13.4 at Kwinana...can't complain.