Here's a couple of excerpts from a post I made earlier this year about these:
From what I understand, most c-clip eliminaors come with thin paper gaskets - the MW ones have No gaskets at all. It's all machined seats with O ring seals in all the right places...very nice design. The Bearing housing seals directly to the axle tube (not the backing plate) All in all, they look like they shouldn't leak. I did use some of the magical "good stuff" as some additional insurance
Make sure you shape the top of the bearing housing to clear the backing plate. You'll understand when you dry fit it - there is a spot on the backing plate that won't let the bearing houseing lay completely flat. Most people beat the plate flat, I personally feel it's better to alter the bearing housing a little. It's nothing drastic and a grinder or file makes quick work of it.
"good stuff" is tha actual name of some sealer goop....you can get it at autozone and I'm sure some other chain stores.