Nearest big body of water to Aycliffe is not for some miles, compared to Marchwood. Also must add that unit 801001(now 801201, assuming you're referring to that) actually ran in service and was running till that extensive length of sit-down, most faults or issues by then would have been rectified due to actual running, where as these are units that haven't even become passenger ready or had the faults fully explored yet ontop of the long storage in salt water environment. Eastleigh units I'd assume would be first ones moving back to metro depots when required as conditions over there would be somewhat better.
801001 actually sat at Aycliffe for just over a year without moving from its arrival at the factory.
It started mainline testing on delivery to LNER!
This unit was originally meant to be first for GWR, and eventually became LNERS after the 9 car bimode and 5 car sets were introduced.
Unit observed (Oct 2016 unsure of arrival date, arrived by road from Japan) as a split set arrived from Japan, and finally left factory as LNER 801201 just over a year later. (10th Feb 2018 I believe it left the factory).
So I don’t understand where you think it was running around before it got stood down for storage.
The unit went straight to store from delivery.
Picture attached below of part of 801001 at Aycliffe as a split set after arrival by road from Japan stored after not turning a wheel on the mainline, where München sat for a year.
. That's if you ever get a chance to 
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