I am assuming you mean the countershaft seal since you said a transmission fluid leak.
Transmission oil would not be leaking from the left side main seal, it would be 2cylce oil and in that case a possible air leak also. Either way the seals are easy to replace.
Counter shaft, Clutch activation shaft, or crank?
If it is the countershaft seal, you should be able to get it out with a tire iron or screwdriver with the edges ground off.
If it is the clutch activation shaft seal, you will need to pull the flywheel & then pull out the activation arm. the seal may come out with it, if not use a dull screwdriver. I should come out fairly easy.