JB water weld. I used it on my hot tub heater pump housing (cracked and leaking) and it's been holding up great.

edit: it also bonds underwater, and is obviously waterproof

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth