Here’s the cover of MAD #189 and the opening splash of the Welcome Back, Kotter spoof in the same issue, both featuring Robert Hegyes as Juan Epstein.

Click on image above to see it at a size you can read!

From MAD #189, March 1977
Cover Artist: Jack Rickard
"Welcome Back, Klodder" Writer: Lou Silverstone
"Welcome Back, Klodder" Artist: Angelo Torres