How to clear the convertible's drain holes
I've searched long and hard and I've not found a "how to" for clearing the drain holes at the front of the convertible cover well. So here goes...
Tools required (Image01)...
1. 1/4" ratchet drive
2. 3" extension (1/4")
3. 6" extension (1/4")
4. 10mm socket (1/4")
5. 8mm socket (1/4")
6. 7mm socket (1/4")
7. 3/8" ratchet drive
8. 3" extension (3/8")
9. 6" extension (3/8")
10. 13mm socket (3/8") - deep socket optional
11. 5mm hexagon head socket (Allen head) (3/8")
12. Snipe-nosed pliers
13. Forked upholstery tool
14. 13mm ratchet ring spanner
15. 10mm ring spanner (ratchet optional)
16. Stanley knife
17. A ground toothbrush to retrim the car without scratching the paintwork
18. Some wood to hold the roof and roof compartment
19. Foam to support front of roof
20. Compressed air supply and hose
21. Water hose
Stage 1 - Preparation
1. Fully lower the roof.
2. Remove the rear seat and store it safely. [Tools 1, 2 & 4]
3. Remove the middle side trim panel (part with armrests) - both sides. Thde two bolts are in each armrest and need to be removed. [Tools 1, 2 & 5] Any trim clips should be removed using tool 13 if possible (see Image02 B). Remove any clips from the car and attach to the trim before refitting. Disconnect the tweeter cable (see Image02 C).
4. Disconnect the slide cover return spring (see Image03) - both sides [Tool 12].
5. Remove the small upholstery rivet (see Image04) - both sides [Tool 13].
6. Remove the upper side panel - both sides. Three bolts (see Image02 A) to be removed [Tools 1,2 & 6].
7. Remove the lower side panel -both sides. Slide the trim upwards to remove. Again remove any trim clips from the car and fit them to the trim. [Tool 13]
Stage 2 - Lifting the roof
1. Operate the roof so the rear of the roof and the opening comparment are as high as possible.
2. Chock open the roof and the compartment (see Image05 & Image06)
3. Using Tool 15 disconnect the hard top attachment and move it aside (see Image07 A) - both sides.
4. Using Tools 7, 8 & 11 disconnect the cover lock (see Image 07 B) - both sides. Be careful not to drop the Allen headed bolts. Note any witness marks for refitting.
5. Release the cables from the catches (see Image08) to allow the lock to be moved aside.
6. Loosen the nuts holding the roof onto the bracket (Image09, Image10 & Image11) - both sides. [Tools 7, 9,10 & 14] Note witness marks for refitting.
7. Support the front of the roof using foam or such like.
8. With the aid of an assistant remove the nuts.
9. Manoeuvre the roof so you can see the drain hole (see Image12).
Stage 3 - Clearing the blockage
1. Attempt to clear the blockage using a hose and compressed air.
2. Test with a water hose.
3. Use the towel to soak up any spillages. Micro-fibre towels are ideal.
4. Use the knife to cut through the sound-proofing under the seats as water is bound to collect here.
5. If you need more access, you can remove the roof bracket. You will need a 13mm ratchet ring spanner to do this [Tool 14].
Stage 3a - Removing the roof bracket
1. Behind the bulkhead (Image11) you should be able to see a 13mm nut. Loosen this nut. Do not remove it yet (or you may never see it again!) 
2. Remove the nuts shown in Image13 and Image14. [Tool 7 & 10]
3. Remove the nut attached to the stud next to the drain hole in Image15. You will need to use Tool 14 to do this.
4. Remove the loosened nut behind the bulkhead. You will be able to use the play in the bracket to get your fingers in the gap to retrieve the nut. [Tool 14]
5. You will have much more access to the drain hole and should be able to clear any blockages.