Loctite 518 for aluminum to aluminum; loctite 5900 for aluminum to aluminum and loctite 242 (blue) if you're going to be in and out of the unit often. Thats from my Loctite Rep.
In the shop we use Valco aluminum colored RTV with their 'tube grip' dispenser. I HIGHLY recommend the Tube Grip if you use a lot of toothpaste type tubes of sealer. You can lay a bead so narrow you can write your name with it in script. Valco is out of Cincinnati and a great company to do business with.