well the letter above has 2015 written on it so they are still swapping these out. i found that via google with someone who had 60 hours on theirs.
here is one in UK, lots of them in USA as you would expect.
yamaha 350hp snapped crankshafts
new flywheel doesn't cure from what i've read previously, just adds more time between failures (80 hours at 3500-4200rpm ish if memory serves) but i don't own one, just getting info while on THT as i seen the post above years ago and had a nosey at the issue.
be happy for OP if Yamaha UK will follow the USA at the very minimum.