Across:
8. There are, in some pianos, trillions of air vents, (or at least one!) (7)
9. Upper class nine suffer from boredom. (5)
10. Lacking force earth is. (5)
11. Am sure to point out, this will tell you the size. (7)
12. The German with a shirt on will eat less. (4)
13. Getting out of bed, pigs ruin slop. (6, 2)
16. Gets nice mix for DNA. (8)
19. Always returns to dream of Paris. (4)
22. Cut off dog appendage. (7)
23. Assorted gravity uses conjecture. (5)
24. Dead serious? (5)
25. Teacher confused...and not very honest. (7)
DOWN:
1. Diana, fearing pointless trouble, became rather common! (5, 3)
2. Heard you got in to taste stew; clever. (6)
3. Quiet transportation to the big cat collection. (5)
4. The compound gets nickel for old students. (6)
5. In an elm chopped up you get some dark pigment. (7)
6. There's a gnu circling round the sun, but it gets no recognition for its achievements. (6)
7. Existence, if in the French. (4)
14. Sounds like you are to go in please; it's fun. (8)
15. Sort of master direction for the ship. (7)
17. Pole or path to the country? (6)
18. Short state has company cloth. (6)
20. Occasions point to outlets. (6)
21. Feeling sorry? Right, left, get the bird. (5)
22. Pen is 100 years old. (4)
The final cache is at N 48 A B . C D E W 123 F G . H I J (where A = 1 and Z = 6)
A is 20 Down 2nd letter
B is 1 Down 3rd
C is 4 Down 5th
D is 14 Down 1st
E is 2 Down 3rd
F is 19 Across 3rd
G is 24 Across 2nd
H is 22 Across 4th
I is 9 Across 4th
J is 25 Across 1st