I have removed a Transom Garboard Plug Flange and it it is not attached anywhere near as well as you might think.
Remove the mounting screws and crank on the plug. The flange adhesive/caulk just shears off and releases; it comes off cleanly!
An earlier Post(#54), he asked if the garboard plug he was buying was the correct one.
I wasn't aware that some boats have garboard plugs on the bottom of the hull amidships.

Is this a standard garboard plug on the hull bottom with the plug head sticking out into water flow?
I can't picture that as being reasonable! Anyone have a picture of one as an example?
So I assume it is a fitting with the flange on the outside of the hull with the plug inserted from the inside.
In which case the Flange Mounting screws are going to be on the outside also.
If drilling out the plug from the outside inward, there will be no need for any Left hand drills.
The plug will screw Into the boat to be removed. Normal right hand drills will do the job.
Once the drill loosens up the plug, the drill will eventually grab the plug and unscrew it INTO the boat.
It is hard to believe that a thread about a stuck plug and some melting ice has gone over 125 posts!
It sure has been a long cold winter!