1) On my -2, the check hole, and fill hole are the same…. Left side, down low…. You can see it in your picture…
2) IIRC, it’s a 17mm Allen. You can get the sockets from VW (Bug) suppliers. They fit a 3/8” ratchet.
3) Fill the side (with a flexible hose) until it starts dribbling out. You can use Teflon tape on the plug.
4) You can just dip the whole transaxle in flex-seal! Just mask off the two output flanges, the breather vent, and the clutch inspection port!
Rocky