The UK Lightning Force will be able to conduct all necessary maintenance of the F-35 aircraft at RAF Marham, including electronic equipment, following aircraft arrival in 2018. When components cannot be repaired on the front line and need to be returned to industry, this will be done via a global network of depots. The global repair network will be adopted by all of the F-35 partners and offers significant benefits in terms of economies of scale and operational availability. It does not mean that components specifically have to go back to the US for repair.
The UK has a through life cost for the F-35, which includes repair costs. I am withholding this information as it has the potential to undermine the UK's commercial position when negotiating contracts with industry.