I guess you're right, TSG. The complete saying we have here is: " you have two chances -- buckleys and none" which, in essence, means: You wont or can't do it, or It wont or will not happen. The phrase came about in the mid 1800s.
Two versions: Buckley was transported to New South Wales in the late 1700s and later escaped. It was considered Buckley had 'no chance' of survival in the Australian bush [but he did - for 30 years]. The other version concerned a bank in NSW named Buckley & Nunn where it was considered you had Buckleys and Nunns chance of getting you money back.
[See also the website www.phrases.org.uk
I tried Radweld a couple of times when I lived in the UK, but, unlike Bars Leaks, it never did the job - possibly because it was only good for weeps and not leaks. Kim mentions that there are 2 types in the US, but here in Oz it appears to be a mixture of both - fluid and small grains. Apparantly it is the grains that get forced into a hole and there solidify. But it does have a limited lifespan. Even so, it's been a godsend in emergencies.