Hi Pam,
I was/am stuck on the same parsings as you.
The best I can tell is...
26a - 1 letter "area" + 1 letter "current" + 1 letter "runs" + 1 letter "centre of Leeds" with the whole clue as definition making it a kind of &Lit.
20d - is an anagram of a word in the clue minus sinle letter answer to 25a.
17a - I'm not sure of this but I think it parses 1,3,4 for "barrels were returned" the 3 for "empty" + 2 for "I'm not sure" - definition is "I can forgo tack"
As for 12a - I don't have a clue:-) Like you say, the answer is clear but for the life of me I cannot see the wordplay!