If it`s your filler plug(s) that is leaking, it`s enough to loosen the handlebar from the clamps to get acces.
You need an open ended wrench to stop the spring retainer from turning, while tightening the filler plug(s).
Check that a alu crush washer is present under the filler plug(s), or better get a couple of new ones.
If you still got a leak problem at the top of the stanchions after tightnining or changing the crush washers, it probably is the o-ring(s) at your spring retainer(s) that is leaking.....not unusual if the springs have been changed and the retainers is mounted back in a hurry.