Times Crossword 25,690 - S or Z?

Solving Time: I breezed through this comfortably in 22 minutes, but on blithely typing and submitting it, was taken aback to be told I had two errors. I do hate it when that happens. What is the point of relaxing with a glass of wine, printing it out, taking the time to parse everything, if you still can't get it right? Hmff. On investigation, I messed up 12ac, so that's one, not a great clue perhaps but still, my mistake. As for the other one, unless I have overlooked something, it must be 7dn, a clue that may well cause widespread 21ac. It's a shame, because there are some nice clues otherwise, like 8dn or 22dn

cd = cryptic definition, dd = double definition, rev = reversed, anagrams are *(--), homophones indicated in ""

ODO means the Oxford Dictionaries Online

Across
1	buckle down - BUCK (dollar) + LED (light) + OWN (to have)
6	spiv - VIPs, rev.
9	grogram - develop = GRO(W) + GRAM, a light weight
10	ticking - jocular cd, ticking being what bombs are wont to do, as well as being a cloth used to make mattresses
12	tip up - I stupidly put top up, but it is, I think, tip up, ie more being left when paying the bill in a restaurant, and to overturn. Not my favourite clue of the day, though I might be somewhat biased
13	inebriate - AT in (W)INE + BRIE
14	leading question - "Who's to be captain?" is a question about leading... the rest of the clue being the def.
17	early retirement - Another cd, although surely an F1 driver would normally have either a retirement OR an accident? Certainly I would normally tend to think of retirements being caused by mechanical problems rather than collisions, though I concede a collision can indeed cause a retirement
20	rare earth - military groups, RA + RE, gunners and engineers, + ground = EARTH, for a rare appearance of a scientific word
21	anger - stove = RANGE, with the R sent to the back.
23	modulus - simple game = LUDO in total = SUM, all rev. Modulus is defined by Collins as "the absolute value of a complex number." Not my field really.
24	all hail - A reference to the witches in Macbeth, Act 1 Scene 3.
25	owed - = "ODE," a poem
26	call it a day - phone = CALL, + volunteers = TA in I'd always = I'D AY. The def. being "Don't work on." A bit of a clumsy surface
Down
1	bagatelle - stone = AGATE + LL in BE
2	croup - it is GROUP, with one stroke missing, the one that turns a C into a G.. Croup is an unpleasant illness affecting children, much more common once upon a time, but apparently still fairly common
3	lord privy seal - my = good heavens = LORD, + little room = PRIVY, + make sure of = SEAL (eg, a victory)
4	dumping - DUMP(L)ING
5	Watteau - pardon = "what" = WATT + letter = "O" = EAU," Watteau being a French painter I believe
7	privatize/ise - sounds like "private eye's," yes, but how shall we spell the answer? Take your pick, I chose a Z and I suspect the setter chose a S. The OED has only Z (Ha! You see?). Collins, ODO and Chambers each have both, though all three of them put the Z version first. Either way, highly unsatisfactory and an editing blunder, it seems to me, not that I care, oh no...
8	vague - Very + AGUE, a fever of which fits are a symptom.
11	corps de ballet - posh girl = DEB + entirely = ALL, in stiff = CORPSE + T(utu). A very neat clue indeed
15	air bridge - *(BRIGADIER)
16	naturally - Friend of the earth = NATUR(E) ALLY
18	Eurasia - is a herb = IS A RUE rev., + A(rea)
19	Ishmael - hidden in hellISH MAELstrom. Easy clue, especially if like me you have read and enjoyed Moby Dick, one of the very great novels of the world, both strange and wonderful. Required reading, not to mention being a good source of esoteric cruciverbal vocabulary.
20	Romeo - Vatican = ROME, + O. That makes Shakespeare 2, science 2.. so a score draw
22	guard - in other words blackguard, vanguard, bodyguard.. another neat clue