Dropping the automatic transmission to access the rear main seal, is it a must to drain the tranny oil or it is safe to drop it with oil in full/normal level?
Tranny will remain horizontal during the process.

 

You have to drain the oil first. Try accessing that seal with all of the oil in it and you're going to have one hell of a mess on your hands.

 

I was capable dropping the tranny without draining the oil, converter was not removed or such.
Just needed access o rear engine wall with RMS replacement.
So can confirm that it was no need to drain the tranny (or engine) oil for this project.