Is the case leaking during the leakdown test or is it just the crank seal?
If it's the crank seals, you do not have to take the top end off to change them,
The clutch side seal is the easiest to change and the hardest to get to, most of the clutch side cover components have to be removed to access it but it has a "collar" inside of it that can be removed and leave space to get a flat blade screwdriver into the inside of the seal and CAREFULLY pry it out of the case. Re-installation needs to be with a deep well socket the same outside diameter as the seal and driven squarely.
The stator side seal is easier to access but harder to remove. It presses into the case and seals directly against the crankshaft. There isn't any room to work any tooling into it without damaging something. The optimal thing to damage is the seal itself. You drill two 1/8" holes (one on each side) into the body of the seal (the thick black part) and screw two machine screws into the seal. Use the screws to pull the seal out and then discard. Re-installation involves lubing the inside lip of the seal and twisting it down onto the crankshaft to make sure the lip doesn't turn out on it and then driving it down the final bit into the case using a deep well socket the same outside diameter as the seal.
