Great fun from Goliath.
Witty, unpredictable and the perfect level of challenging. Many thanks to Goliath for the fun. And wishing everyone a happy New Year.

ACROSS
1. Radical socialist leader in tears (8)
SWEEPING
S[ocialist] (leader) + WEEPING (in tears)
5. Unconventional exit (3,3)
WAY OUT
9. Stuff seen in a horse’s bowel and elbow? (8)
ANAGRAMS
RAM (stuff) seen in A NAG’S (a horse’s)
10. Feature of some bacon meat about right (6)
STREAK
STEAK (meat) about R (right)
12. Misappropriated wrap (5)
STOLE
13. E? It’s a revelation! (3-6)
EYE-OPENER
Cryptic definition
E[ye] (opener)
14. Trouble for canines and heartless bears (6)
CARIES
CAR[r]IES (bears, heartless)
16. Sir sent back German dish (7)
RISOTTO
SIR< (<sent back) + OTTO (German)
19. What was in the beginning red hot flowing around water source (3,4)
THE WORD
(RED HOT)* (*flowing) around W[ater] (source)
Biblical
21. Passion in higher education for all (6)
UNISEX
UNI SEX (passion in higher education)
23. Skill shown when confined in lift (9)
CARPENTRY
PENT (confined) in CARRY (lift)
25. Are you saying pen is past its best? (5)
RUSTY
R U (are you, “saying”) + STY (pen)
26. An Arab boat with bells on (3,3)
AND HOW
27. Push one’s luck and request computers (3,3,2)
ASK FOR IT
ASK FOR (request) + IT (computers, Information Technology)
28. Fancy some popcorn? A teacake? (6)
ORNATE
[popc]ORN A TE[acake] (some)
29. Obscure secretion not quite in order (8)
ESOTERIC
SECRETIO[n]* (not quite, *in order)
DOWN
1. Thin and extra small included (6)
SPARSE
SPARE (extra); S (small) included
2. Raise flag, speak and disappear (9)
EVAPORATE
PAVE< (flag, <raise) + ORATE (speak)
3. Pegg is clean (5)
PURGE
Cryptic definition
P+EGG = P+URGE
4. Book of anaesthetics (7)
NUMBERS
6. Against drinking beer on street, for starters (9)
ANTIPASTI
ANTI (against) drinking (IPA (beer) on ST (street))
7. A once troublesome Indian, perhaps (5)
OCEAN
8. Establish a trek winding westwards as well (4,4)
TAKE ROOT
(A TREK)* (*winding) + TOO< (as well, <westwards)
11. Ultimately, pub clientele there for this (4)
BEER
[pu]B [clientel]E [ther]E [fo]R (ultimately) – semi &lit
15. Made smooth like De Niro? (6,3)
IRONED OUT
Cryptic definition: reverse anagram: (IRONED)* (*out)
17. Variable rate safer, says financier (9)
TREASURER
RATE* (*variable) + SURER (safer)
18. Toccata’s unusual musical notation (8)
STACCATO
20. Go out for fruit (4)
DATE
21. July’s session covers epic hero (7)
ULYSSES
[J]ULY’S SES[sion] (covers)
22. Magical writer’s short wand (6)
MYSTIC
MY (writer’s) + STIC[k] (wand, short)
24. Fluid and/or gas (5)
RADON
25. Second installation of fine art not an abomination (5)
REFIT
(FI[n]E [a]RT)* ( not AN, *abomination)
Couldn’t parse PURGE. I’d forgotten that Goliath does this sort of thing. Nor could I parse ANTIPASTI as I’m not into exotic foreign beers. Didn’t think much of the clue for UNISEX. The clue for TAKE ROOT would have worked better as an across clue, I thought. ANAGRAMS took me a while.
Lots of good clues made for an enjoyable crossword. Shame about 8d though. I assume this was originally written as an across clue and wasn’t picked up in editing. So easy to change ‘westwards’ to ‘northwards’ or just ‘up’.
Oh dear! I went off on completely the wrong track with 25a. Once I’d seen the middle two words together I was stuck! 😂