Mine failed. It got very stiff. When I dropped it to deck level the two halves of the unit wobbled and bits of delrin bearings fell out. So do try washing first - with hot water only and see if it frees up. But try the wiggle test. Don't know if the Mango top swivel is the same/similar to the Santorin. I had to detach the bottom of the forestry to slide mine off. Inside are two plastic plugs which you remove and pour out the delrin bearings. Mine were 10mm (actually 9.5) and I bought 2 packs of Harken 10 mm bearings. You feed them in through the plug holes and they keep the two halves securely together- provided you replace the two plugs. It is a simple and robust system that Henri may have carried over from the Mango.
Ocean Hobo SN 96 on the hard Grenada