72 hour free transit advice needed

i am in qingdao, with a return flight back to the UK (via wuhan) on the 16th of august. my visa is an x-2 type with a single entry. i have to attend my brother's wedding in korea on the 13th of august and am hoping to return to china right on the 16th to fly back to the UK. unfortunately, given my visa is single-entry, i probably wont be allowed back in to catch my flight without another visa.

is the 72 hour free transit the best option for me?
can i apply for one in seoul or will it have to be done at the airport when i return from seoul?
i understand that with such a visa, i have to fly directly from the airport i arrive at, does that mean that i have to return to wuhan rather than qingdao given that my return flight stops in wuhan before continuing to paris?

all advice and help much appreciated. big fan of the wonderfully informative work done at travelchinaguide.