Firstly, you need to be sure that the problem is the water pump. Why do you think it is the water pump? Do your cooling fans come on as they should? Is there a leak from a hose or a leak from the water pump? I would do a pressure test of the cooling system and establish what the real problem with your cooling system is. Does you Audi consume coolant? How old is the radiator? have you done a block check to verify your head gasket? Also, this vintage Audi is very tricky to get air bubbles out of the cooling system which can cause an over heat problem, there is precise way to bleed these engines. Please be sure of the pump, so you don't waste your time and money.