The issue with AMS-S-8802 B2:
While AMS-S-8802 B2 (e.g., PPG PR-1440 B-2 or Flamemaster CS-3204 B-2) is a highly durable, fuel-resistant aerospace polysulfide sealant, it is
not structurally compatible with untreated HDPE. Like most sealants, it relies on specific surface energy to bond, and HDPE's naturally low surface energy makes it extremely difficult to adhere to without special preparation.
If you choose adhesive route - these are structural adhesives and specifically designed for bonding with HDPE and do not require any pre-treatment beyond clean surface with alcohol, sanding it would be even better:
1. 3M Scotch-Weld Structural Plastic Adhesive DP8005 (medium viscosity)
2. Permabond TA4605 Polyolefin Bonder (gel consistency)
Those could be applied as preventive care over entire vent surface to seal it off.
I will test both on empty glass cleaner container (HDPE). The key is adhesive bond strength with HDPE (low energy surface) and elasticity - this is where epoxy fails. JB weld is brittle and it snaps like a match stick on bending and it is not structural adhesive type. So no wonder it failed on me 2 times. I hope epoxy removal will be easy, as it really could not adhere to the vent HDPE substrate.
I am pretty good with plastic welding, but I am not very comfortable with using plastic welding method on fuel tank due to fire hazard, as it would require full evacuation of the gas from the tank, removing fuel pump and drying it off. Also you can not use plastic welding as preventative care as you could potentially damage working vent while applying extra material over the vent surface and it would be very time consuming activity.
As you can see my endoscope already celebrating 4th of July
