" To answer the risk question, numbers of amps (or milliamps)
that are leaking down the safety ground wire must be known. "


If I had an espresso machine that was tripping a GFCI and I determined
it was not the GFCI, I'd either get it fixed or get a new one. Exactly
how much current is leaking has very little relevance. Clearly there
is a defect and the current could change from a very small amount to a
lethal amount with no warning. If it's a loose wire, or partial short,
it could go to lethal just with moisture or a good bump.