After being sure the right tank is leak free I could remount it to the wing and start a second leak test for the left tank.
Mounting the wing is done easy by putting it on 2 wooden blocks first:
The tank is mounted to the main spar with AN3-3A bolts. Due to the shims I needed a longer bolt (AN3-4A) for the second bracket. With the endoscope I checked the bolts:
Next I did a soap bubble test on the left tank:
Next is another fuel test with the water manometer.
See Fuel tank leak test for more info.