Fareastdriver, just noticed this in your post:
A 500kg saving by rewiring it I would have thought was a bit optimistic
Its not a 500kg saving, it is a 500kg increase in effective payload, comprising roughly 100kgs saved due to rewiring and 400kg from upping the MAUM from 7000kg to 7400kg routinely. The Mk1 can go to 7400kg, but only in a couple of limited instances, which does not include routine trooping. The plan for theMk 2s also includes the 5th tank, but not sponsons unfortunately.
Wrt airframe hours, even the Mk1 fleet leaders are only just over halfway through their airframe lives, it has taken 35 years to get that far, the next 10 are unlikely to take it to the limit.