If you have been using an rtv based sealer that is your problem. It should be an anaerobic type. Also hopefully you have not been using anything aggressive to clean the aluminum "housing". I use loctite brand "case sealer" on all my stuff. I have a tube on my bench at work, can't think of the number for the life of me at present. I will look tomorrow and forward it to you. Also clean is the thing, I wipe everything down with laquer thinner prior to assy.

ps--if the mating surfaces are out of whack, you can dress them up on a piece of 400 wet/dry (wet) on a piece of glass...