Originally Posted By willie_68coronet
I got the synthetic one and it seals perfectly on the aluminum napa neck and mp housing. The thicker one is for a not so flat surface I think.


That would be correct and thanks for your support willie!

I have even used the chromed pot metal housings with our MP-15 gasket without issues. HOWEVER...... the housing was milled flat. Even brand new they are warped beyond belief rolleyes