Is there a list of known leaks within the iPhone SDK sitting somewhere, all alone?
I guess you would have it specified by version. (I just ran my test app - it has a leak outside the project itself (somewhere related to connections) when testing it on a v3.3.1 iPhone 3G, but the leak is not there using an iPhone 4 v4.0.2.).
It's doubtful that there's a public list of known memory leaks. If you want to know whether your leak is a known issue, your best bet is probably to search Open Radar, or to use Apple's Bug Reporter and see if you get a response.
During my short experience with the iPhone SDK, I have never encountered a memory leak caused really by the SDK. It is mostly caused by your code but has shown itself later.
It is also possible that the new SDK has improved some ways of doing things, so that your previous leaks do not occur anymore.
You need to give more details to the leak in order to help you.