Maybe the science on this has changed? The display I saw when I visited in 2016 says they attribute significantly accelerated deterioration to the choice to spray the vessel with PEG.
When I was a kid in the 80's I visited the old museum where they were actively spraying the ship, and I think they took that decision in the 70's, so I wouldn't be surprised if they know a lot more now about wood conservation.
Anyway, I think they're saying now that the biggest problem is that the old iron is reacting badly somehow, and they're thinking about - very carefully - replacing all the nails.
But the whole thing is very much a work in progress when it comes to conservation, no-one has done anything like this at this scale ever.
Some discussion on this at https://www.acs.org/content/acs/en/pressroom/presspacs/2012/....
But I'd certainly believe them if they've changed their estimates.