Hi ACfly,
Thanks for the report.
I do not think you need to go back through security ( I think there might be a "super secret"
walkway back to T5A- the " super secret" being it is not publicised- I think there is a post here detailing it.
I was able to get a shower with no waiting in Galleries F on a Monday afternoon but on my outbound in August the only time available was just when I was due to head to T5B .
Regards
TBS