If the Devs know there is a leak they should fix it [img]/images/graemlins/smile.gif[/img]
For memory leaks - it helps to use a steady state test.. I have used an increasing load test in some cases. If the application under test fails with an error or exception related to memory utilization you surely know its a leak...
Try isolating various sections of the application to identify leaks.. We once had a leak in the login process - which got hidden in our test since we only logged in once and concentrated on repeating other actions - we needed to run a Login-Logout kind of a test..
Finding leaks is a great challenge and during this process try to create a set of workloads which would cover most of your application features, it will greatly benefit you in future..
Try creating dumps in the background using WinDBG, ADPlus or DebugDiag if its a Windows app... You could get them from MS - Debugging tools for windows.. Most applications should have similar tools for in-depth analysis..