Parply

So it seems like I have the shock knock problem with my 57 STi PPP. Bought in Jan this year with 32K on the clock. I was told by the garage it had original shocks and lowering springs. Now done 35K and for the last few weeks there has been a clunking sound from the rear passenger side at slow speed. It seems to be getting progressively louder. The limited warranty has already expired so I cannot go back to the garage and it is half way across the country anyway. I was already planning a long list of upgrades but it seems like the suspension is keen to be top of my list. My questions are how do I confirm it is the shocks, how long do I have to save up, and what will happen if I wait too long ? I was looking at the ScoobyWorld stage 3 performance handling pack as the way to go anyway but I'm open to suggestions. BTW it's not worth suggesting I get my hands dirty as a life time of experience tells me that this would only end in tears and a larger bill from the garage.