i have been a user of the mooncup UK for 2 years. i have tried the divacup and the ladycup and always go back to the mooncup because i simply love it. however, a few months ago i started experiencing leakage on my heaviest days (but only while sleeping at night). even the pantiliner wasn't enough to stop the huge leak. i'd take out the cup and it would be completely empty! during the daytime, though, it's a completely different story. i have no leaks and it works textbook perfect.
coming on here i've heard advice such as: make sure it's positioned properly! check the seal! try a different cup! none of those solutions worked. on my own, i have found a solution. on my heaviest days, i have figured out that if i sleep with a pillow under my side (i sleep on my sides for the most part), so that my back is as straight as possible, i will not leak. i have been successful with this for 2 months now. i am far less paranoid at night. (of course, besides trying this, make sure your cup is positioned properly as well).
i hope this helps some of you out there!