Like using teflon tape on a compression fitting

[FJ_Hooligan]

Or, use a couple of dabs of grease to hold them in during assembly.  The grease will burn off quickly.

[Old Rider]

Many good sugestions i did the ovalshape trix and it worked out perfect.Also i did not try to fit the gasket good enough first time i did not put it deep to the bottom of the hole witch has smaller diameter.