Kekkou Kamen

These series both have extremely scantily clad magical girls, complete with transformation scene and cheesy plotlines.  

Both shows are about under clad masked super-heroines protecting a girl in high school from mobbing and abuse. They came out in the early 1990s and share a similar narrative and artistic style. What little cloth they wear has resemblance, e.g. the feather on their headgear. Gootaman is closer to Mahou Shoujo, Kekko to the superhero genre. Gootaman is shorter, and it's plot could without much problem be made into a Kekkou episode. Kekkou is the more raunchy, zany and better show. 

Both are by the same mangaka, in both we see peverted teachers taking advantage of their students. 

This is basically the same thing. One naked justice warrior fight the oppressive students. The only difference is that is shimoneta the society is completely focus on purity and no dirty thoughts and the purpose of the female naked warrior is to liberate boys and girls. While the ova kekkou the society is corrupt and lusciously and the naked girl is liberating from that.