GMS 18.3.1 download available - let's start ...
Not now. Because upgrade is a little bit more work than usually, it will happen later. This evening I will try to update GMS in my test environment which is based on OES.
I see additional posts here where GMS on OES is discussed - I run a working installation. For years now. This test environment has been started with old OES versions and with old GroupWise versions (Messenger and Vibe too). It has been upgraded over the years. GMS has been on board from the very first time.
However I had to use more than one ip address - each service one ip address because these services sometimes fight for the same ports.