No 12999, Tuesday 28 Jul 2020, Vulcan

Solution to 7D has been deliberately left unsolved and is to be answered only by a non-regular/novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.

ACROSS
1   It’s corrupt, with governor bringing downfall (12) OVERTHROWING*
10 Fought against work discrimination, primarily with sit-in (7) OPPOSED {OP}{POSE}{Di...n}
11 He delivers stories to read (7) NEWSBOY [CD]
12 Museum and university very involved in traditional knowledge (6) LOUVRE {LO{U}{V}RE}

13 Start hostilities around where it's flaming hot (4,4) OPEN FIRE [DD]
15 Criticise books defending party’s rebel (9) DISSIDENT {DIS}{SIDE}{NT}
16 Drink is sent through corridor (5) AISLE {A{IS}LE}
17 Launch of new outlet shortly coming about (5) MOUNT {MOU{N}Th}
19 Fruit of Argentine variety (9) TANGERINE*

22 Last month I have in Spain with kids (8) DECEIVES {DEC}{E{I'VE}S}
24 Poems on South American city (6) ODESSA {ODES}{S}{A}
26 One who keeps away from say, entertaining old minds regularly (7) AVOIDER {AV{O}{mInDs}ER}
27 Show is about Republican framework (7) TRELLIS {T{R}ELL}{IS}
28 It is pressmen turning into PR agents (12) SPINMEISTERS*

DOWN
2   Very beginning of autumn rains and mists (7) VAPOURS {V}{Au...n}{POURS}
3   Stop and shower, time to show self-discipline (9) RESTRAINT {REST}{RAIN}{T}
4   Foolish idea keeping leather (4) HIDE [T]
5   All-powerful top men? Not one that’s sorted (10) OMNIPOTENT {TOP+MEN+NOT+1}*
6   American, one working outside Washington (5) IOWAN {1}{O{WA}N}
7   A device, small needle tip to pierce all around (7) G?B?I?S (Addendum - GUBBINS - {S}{BUG} over{NIB}<=  See comments )
8   Dismissed as flashy/pronounced (6) BOWLED (~bold)
9   Variables associated with reportedly thin solvent (6) XYLENE {X}{Y}{LENE}(~lean)
14 Two containers for an instrument (10) KETTLEDRUM {KETTLE}{DRUM}

16 Addition of a couple of guys during day time (9) AMENDMENT {A}{MEN}{D}{MEN}{T}
17 Insane when relatives basically in town (6) MADRAS {MAD}{Re...s}{AS}
18 University to meet after the end of session — to change position (7) UNCROSS {U}{s...oN}{CROSS}
20 Dirty urinals with water all around (7) INSULAR*
21 Pass drinks during the middle of meet (6) ELAPSE {mE{LAPS}Et}
23 Creature seen in part of Asia, mostly around river (5) INDRI {IND{R}Ia}

25 A case of free tuition (4) ETUI [T]

Reference List
Work = OP, University = U, Very = V, Criticise = DIS, Books = NT, New = N, Spain = ES, South = S, American = A, Old = O, Republican = R, Time = T, Small = S, Variables = X,Y, Day = D, River = R