K-Seal Coolant Leak

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2008 Mazda5 GT
2008 @ 135K.

Radiator developed a slow but continuous leak, right above the drain plug (near lowest point); pour coolant in, it comes right out in a slow/steady trickle. Thankfully I was able to catch it while I was on the road (thank god for temp gauge) and had to shut it on/off and limp my way home to prevent overheating. Tried a bottle of K-seal and it works even on our plastic radiators. I was concerned it was formulated for meatal radiators b/c the liquid has a metallic/copper-ish sheen to it. It seal up and no leaks and is advertised as permanent fix. Hope this anecdotal feedback can be helpful to someone who might get stuck. Holding strong for the last two weeks and took a few hours long drive. If it can hold till warmer weather, that is a big win so I can address it later.

FWIW, I got the car up to temp before I pour in the k-seal (extra coolant and distilled water on standby). Shake well, pour in, let idle for 15-20 mins. Note this will not fix your head gasket leak, they have a different solution for that.
 
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2010 Mazda 5 Sport
Sure if you're desperate, it can save the day. But don't think it's a permanent fix.

Modern radiators are plastic and just crack over time so this problem is most likely going to resurface.

I would do a coolant flush and replace your radiator.
 
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2008 Mazda5 GT
Update. Sealant was good for about 1.5 month. Leak returned but went from slow trickle to very slow drip when parked/cool. Ran coolant dye and seems the engine oil cooler gasket is also leaking.