Modern Vespa

Are those the cheapo garden hose type of clamps, whose cut threads go all the way through the steel? If so, no wonder they leaked. The correct clamps have stamped threads that do NOT go all the way through, so are much stronger and can properly compress the tough rubber of coolant hoses.

Nice contribution!

No, it was the Piaggo-installed squeeze-type hose clamps. Thus far, I have had 3 fail on my BV350, and now three have failed on the Vespa.

I have absolutely no faith in the factory hose clamps. Cheap garden hose clamps are an improvement as they actually work

Actually the Oetiker clamps are pretty damn good - if the right size is used with the right material. PEX plumbing is all done with them - and those joints never leak! They are also the Right Thing to use with high pressure fuel hoses and air conditioning systems in cars.

However, Piaggio have used them with hoses that seem to compress and loosen over many heat cycles. The clamps are good - the implementation is crap. The pressures in a Vespa system aren't even that great.

So Jubilee clips (or equivalent) are the way to go. If the clamps cost less than ~50 cents each, treat them with suspicion.

I came across another old thread that has lots of pictures on the removal process. Linking here for reference:
remove the floorboard