As much as I might agree with sentiment of that post, I don't fancy the useful resource that this thread is being locked. I don't wish to backseat moderate but I think that's best left there and ignored.
As much as reusing Pistoia for UK stock concerned me at the time, if there's one country I would suggest to take it over, it would be Japan, and if there's one company in the rail industry I'd trust to do it, it would be the co-manufacturer of the Shinkansen units. That's all that stopped me doom-mongering about use of the plant when it was announced.
As jimm points out, even if rather curtly, the evidence we have so far is anecdotal, realistically we'd need someone who works in or is close to the maintenance division at GWR to comment on the comparable failure rates of 802s vs 800s on a per-unit basis, so the pre-series Japanese built units can be excluded.
New units having technical problems is par for the course, but when it's things like components being fitted back-to-front that is inexcusable, alarming, potentially dangerous and, realistically, typical of what AnsaldoBreda used to be famous for. It it's an issue that's come up a few times on 802s and not 800s, then it suggests Hitachi's management of Pistoia isn't as effective as it needs to be, yet. That of course, is all an if, without the data it isn't really possible to comment.
It could just simply be that across the board Hitachi's manufacturing isn't that good, but I find that hard to believe.