to refit the pump, engine needs to be 10 degrees after top dead centre, and the pump needs to be set so the nick in the gear is at 10 o clock. turn the pump on until there is pressure, then install. the fine adjustment needs to be done via diagnostic computor though.
it may be an early one, where there is a 17mm headed blanking plug in the pump. these need a tool from mercs fitted to lock. £9 it costs.
bit of an expert job either way
tony friel
November 2011