The cracking of one wing spar was discovered on an aircraft being used for cyclic testing. The cyclic testing had accumulated the equivalent of 20 years of operational service towards a longer life goal. The problem has been identified as a design problem and not a subsequent manufacturing processing problem. Correcting the design will add one half pound to the weight of the spar. Of course, all assembled and deployed aircraft will require retrofitting the new beefed up spar at a convenient time, lets say short of 20 years.
The wings are bigger on the F35-C version than either the -A or -B versions. I would think the UK version would be good to go by 2018 assuming nothing goes wrong between now and then. Anyhow, what could possibly go wrong between now and then?