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[Linked Image from i.pinimg.com]

From MACHINE MAN 6, Sept 1978, and other Marvel titles the same month.
Another ad by Cockrum for the X-MEN monthly series, re-cycling a page from X-MEN 107.


There's a third house ad by Cockrum in the same period, in MACHINE MAN 2 and 3, ETERNALS 18, AVENGERS 165 and IRON MAN 118.
And shown here in MARVEL TEAM-UP 79 (March 1979).
https://viewcomiconline.com/marvel-team-up-1972-issue-79/

I guess when you double the frequency from 6 issues to 12 issues a year, you want to make sure the thing's going to sell !