So after having to do this twice on my Mk2 Focus (2005) in the last 18 months, I figured I would make a guide for anyone who experiences the same issue. I managed to piece together various forum posts and Haynes manual pictures to do this, I don't think there is a comprehensive guide (if there was, the photobucket issue will have more than likely effected it anyway!). After taking a lot useful information off this forum, I am giving back by making this guide as my first post.
The symptoms first appeared in the form of my radiator fan staying on after the engine was turned off. After checking the coolant level (assumed that was the issue), it had dropped by more than half and at the same time had noticed a soggy driver's mat. Under the mat was a 'puddle' which, from the colour of the liquid, I discovered was engine coolant. Again after some inspection and forum digging I discovered one of the pipes coming through the bulkhead into the heater matrix (bottom of centre console) was leaking. This was due to a ruptured o-ring where two pipes join together.
The leaked coolant after topping up the reservoir then driving home form work.
The 'culprit'. Leaking coolant pipe join and the plastic clamp has popped off.
If having the work done at a garage, they will more than likely result to dismantling the entire dashboard and replacing the heater pipes and/or matrix resulting in a very large cost mainly due to the labour involved (£400 plus I read people were getting quoted). The guide below requires just the cost of the Ford parts (around £15), 5 litres of coolant (£20ish), and about 2 hours of your time to replace the o-ring that causes this problem.
Step by Step Guide
1. First off you will need some o-rings and pipe clamps. I have read in multiple places that only the actual Ford parts should be used due to incorrect sizing with other branded parts. I highly recommend purchasing at least 2 o-rings if not more as the first time I did this, I dropped 2 behind the centre console, never to be seen again. Ford part nos. 1342708 (o-ring) and 1454337 (pipe clamp).
2. Jack up car onto axle stand(s) and remove engine under tray (see Haynes Manual).
3. Drain coolant entirely by removing crosshead bung screw at the bottom right (nearside) of the radiator (remove coolant reservoir cap to increase rate of drain).
4. Remove/undo rubber heater pipes where they meet the metal pipes at the engine side of the bulkhead (Pics below). I only removed the top pipe as I could not access the bottom release clip but it happened to be the one that was leaking so worked in my favour. The clips require a 30o turn anti clockwise and pull off. The pipes swap orientation once through the bulkhead i.e. top pipe engine side becomes bottom pipe cabin side and vice versa.
5. Remove the driver's side dash panel, next to the clutch pedal, held in place by one T25 screw under a little cover. You will likely need a friend for this bit as they will need to pull on the engine side of the pipe whilst you lie in the driver's footwell and pull the lower part of the leaking pipe to split it at the join. The lower pipe inserts into the upper part about 1 inch. At this point you will see the ruptured o-ring which resides in the upper part of the pipe. Remove the old o-ring with a flat blade screwdriver (See pics below)
6. The most difficult part now, inserting the new o-ring. I found the best way to do this is looping the new o-ring over a long flat blade screwdriver and pointing in an inch or two into the upper pipe so that you hugely reduce the risk of dropping it. There is a slight recess for the o-ring to sit near the lip of the upper pipe. Using the large screwdriver to hold it steady, guide the o-ring into place using either your other hand or another, smaller flat blade.
7. With the o-ring finally in place, you will need your friend again to push on the engine side of the pipe whilst you guide the two split parts back together as closely joined as possible.
8. Finally, you will need to wrap and clip the pipe clamp around the join. This can be quite tricky as the join must be 100% flush and the clamps will only hold in place once clipped properly. This is best done with the aid of a pair of bent nose pliers. It should be tight and difficult to twist/rotate once clipped properly.
9. All left to do now is to re-attach the rubber pipes from the engine side of the bulkhead and refill the coolant reservoir. You will want to overfill the reservoir right to the top as when you start the engine, coolant will be sucked into the cooling system and dramatically reduce the level. Refill as necessary to the correct level and leave the engine running for 15 minutes and check for any more leaks in the cabin. If all is well, there will no longer be any leak at the join in the cabin. Job done!
Let me know if you need any help if you have the same issue or have any questions/suggestions regarding the guide.