That a molded rubber gasket which is suppose to be press fitted into a CNC machined cavity. Chances are either the CNC process is incorrect or the elastomer molding is faulty. Best bet is to contact
sigelei and see if the factory (Representative/Distributor or place of purchase ) will support your claim.
If all else fails, could take the unit to a gasket shop fabricator in your *area and
pay them ($5-10 is reasonable if possible) to secure the gasket to the metal housing.
*Could fill in your location, it may help you in obtaining location specific information to your question(s).
On the top right hand corner of this post you will find --"your name" next to "Inbox and Alerts"
Place the mouse pointer on your name. You will get a drop down and on the left hand side of this drop down you will find "Personal Details". Click Personal Details.
In Personal Details, in middle of screen in gray, you will find "Location" Could fill that box line in.
re:
https://www.e-cigarette-forum.com/forum/threads/new-users-put-your-location-in-your-profile.2889/