wtf, that pump is listed for MK2 8v/16v GTI on GSF as well, and if so it should deffo have 2 outlets on it. What a load of muppets GSF are:
17058 WATER PUMP-COMPLETE G2 GTI / 16V 8/83 > 18.25
maybe its this one you need:
17058A WATER PUMP-COMPLETE VW/AUDI 1.5-2.0 PETROL+1.6D-1.9TDi 81>** 29.95