no you wont see it by removing the pump you have to remove the RH casing, be careful of the shim washer that always falls off the peg at the front
a few tips
Drain the oil, if its good oil clean around the drain plug first and drain it into something clean...and then you can re-use it (your choice)
undo the rear brake rod adjuster and use some string / cable tie around the arm and footrest brkt to hold the lever down out of the way
disconnect the pipe to the oil tank and jam it in the cylinder head fins, if the bike is on it's side stand no oil will come through (but check)
you may get away without disconnecting the awkward to remove pipe from the pump to the carb if you pull off the case and invert it and tie it up...see pic
dont forget the hidden case screw behind the pump cover
dont forget to replace the shim as mentioned earlier on re-assembly
how about drawing a line on some masking tape that indicates the 2 stroke oil level and monitoring that?
The seal in question is behind the plastic drive gear, heres the case tied up to save work
If your case gasket is in good nick like the one in the picture...hey you can even re-use that...another scotsman showed me ...If not.'Wemoto' sell them individually, or at least they did do