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First I would reset the toilet just to be sure the wax ring isn't the problem. I would use a "no-Wax" ring also instead of a wax ring.
If that doesn't fix the problem removing the leaking joint can be a chore. If it is leaking at the joint it probably wasn't primed properly, which could be good. Now I haven't seen your plumbing so....to get the pipe out of the leaking joint go about 24" away from the 90 if possible and cut the pipe square. With some movement, if the joint isn't a good one, the pipe may come out. If it doesn't remove the toilet and replace the floor flange, 90, and short piece of pipe and reconnect.
Hope this helps, please reply with any other questions about this.