What powder are you using that "leaks like a sieve" with your auto-drum?
Using AA#2 - which is about the finest grained ball powder I've tried, mine leaks just a tiny bit - like 3-4 grains per 100 throws.
If yours is leaking more than that I suspect something is wrong with it.
Have you contacted Lee about it yet? I haven't had to use it but I've heard their warranty service is excellent.