with one of my previous cars, the mechanic put non factory pads on. every now and then whenever i brake i will feel a shudder in the steering and clunking noises. As soon as i put oem pads back on it...
take off battery terminal for about 5-10mins. reconnect it. drive on long stretch of road to 60km/h then let the car slow down to complete stop without brakes. repeat about 3-4 times.
did you spill any coolant around it anywhere. it's alright to drive around for now i guess. but if there is a crack it'll just keep on cracking. you'll end up losing alot of pressure and power.
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yea sounds like it. you can't see whereabouts it's leaking out of? get someone to block the back of exhaust and have a look at the headers to source the leak
even if the owner fixes the faults. other problems will arise because the owner neglected it. end up being a money pit because you're always in need to fix it.