The 100 & 150 are really the same airbrush, the only difference is the actual body itself. Trigger, valve, head etc. are identical.
Pull the needle first and put someplace where you won't damage the tip (or damage yourself WITH the tip!) and unscrew the head assembly from the SG, you should be able to remove the entire assembly without breaking down the individual parts. There is a teflon washer (50-055) that you must be careful not to damage or lose! The beeswax goes on the threads that attach the head assembly to the body (50-0381). It's not strictly required, but it goes a long way to avoid leaking. You don't want to overtighten the head as it crushes the washer.
DO NOT remove, damage or lose the Teflon Needle Bearing (50-046)! That is a part that Badger suggests the user does not replace, as improper installation can cause the needle to be out of tune. If you lose that part, or damage it, they suggest returning the entired airbrush to them for installation. Which isn't a bad thing as they tend to tune up the brush when it's there. You do have to pay shipping both ways, I believe. I've never had to do that (knocks wood). Yet!
I've included a partial of the "exploded" view of the AB.
The rest of the parts can be found
HERE.
Good luck!