The only practical way of fixing that seal is to split the case.
You MIGHT be able to extract it after only removing the crank's beveled-gear, but I sure have never had luck doing it that way. In any case, if it's as you described, you'll need to buy a new seal...they come in pairs, and it'll put you back about $10.
There is absolutely no need to split the case to install a seal on these motors!
You can buy seals individually at $3 from many places.
The right side bevel gear side seal is the thick one. The thinner one goes on the magneto side behind the magnet.
You will also need the gear puller tool.
Use a sharp pointed tool to extract the old seal.
Use a socket that is a bit smaller than the diameter of the seal
to push it straight into the case.
Lube the seal with oil.
Check the shaft that it has no sharp edges that may damage the seal.
Might be easier to replace if you pull the clutch off.
Do you have mechanic tools in metric?