You can likely repair the tank with a soldering iron. Test if it's thermo plastic or thermoset. If the former, you can melt the crack back together.

Another trixk that works is cut strips of a thermoplastic (I used to use Pringle lids before they made them the useless clear ones that don't seal). Light It on fire and it will drip hot enough liquid plastic it will meld Into other themoplastics.

I've used that trick many times to patch water pumps on washing machines that self destruct when a dime gets in there. The fix is water right and good as new.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)