hier gibt´s Ersatz:
Note for plastic tanks
The materials we use is from the best on the market but during the time about 10-12 years (depend of use) plastic tanks polymerized and make porus with result to make bubbles on stickers from the gas pressure.
Unfortunately is not exist any solution for this problem even if the stickers is thick as OEM.
One easy way to see if you have porus on your tank is to take a piece of any color vinyl 10x10 cm from your closest sign shop and place it on the right side of tank at the top (not on top of the old decals or on the left side)
Leave your bike at the sun for 2 hot days and you will see if the gas tank has porus.