I'm in the process of removing a turbocharger from a VW T4 1.9L TD (non-TDI). The turbocharger is secured with 4 very unusual screws; they look like an external splined drive with a diameter of approximately 14-15 mm. The heads of the screws have 5 holes arranged in a pattern like a cube. Can anyone tell me what kind of tool I need to use for these, and perhaps where I can find one?