I think it will be caused by loss of clutch fluid, the symptoms would indicate failure of the clutch to disengage properly. It could be leaking out of the clutch slave cylinder which is in or on the gearbox.

Thanks for the suggestion. Are the brake and clutch fluid likely to be combined ? If so, the brake fluid reservoir is not far off the max and it looks orange/red in colour, whereas the stuff dripping is most definitely dark brown in colour.

the pipe you show is the Air Con condensation drain. Check the colour of your engine oil I suspect you may be leaking engine oil into the clutch assemble and the clutch is now polluted and dragging. Can you select all gears with the engine off. If so then you have a failed rear crankshaft oil seal. Regards Peter

Thanks for the pointer on the clear fluid - I thought it might be unrelated so it's good to know for sure.

I didn't think to check the engine oil level/colour, as the fluid smelled so bad/distinctive that I presumed it wasn't engine oil, which I have dealt with in the past.

Funnily enough I was able to select all gears with the engine off, yet struggled to get it into reverse to back it out of the garage this morning so I'll bear your suggestion in mind.

Edited by mikej on 28/10/2011 at 19:30

Why are you driving it. There is something clearly wrong. It could be gearbox oil which your explain the smell but not the colour. Engaging all gears when the engine is off indicates a polluted clutch form the oil leak. Regards Peter

Update - I've heard back from garage, who took the gearbox out yesterday – the diff is knackered and gearbox casing is badly damaged which has caused the gearbox oil to leak – basically, the gearbox is scrap. Oil has also contaminated the clutch.

A fully inclusive price of £1204 gets me a second-hand 6-speed gearbox (from a 2007 car with 32k miles - 3 month warranty) and a new (3-piece) clutch. My car was a 2005 with 54k miles, so at least this gearbox is newer I guess.

Quote for a reconditioned/exchange gearbox (with 12 month warranty) plus new clutch was £2k ! (Car is worth £3-4k max)

I can't help thinking that this catastrophic gearbox failure is linked to the acceleration/decelleration jerkiness issue that this car has suffered with ever since I bought it. The dealer changed the engine mounts under warranty which didn't help.

A friend of mine has a theory that a faulty clutch (springs?) might lead to abnormal wear on the gearbox which could end up causing something like this. Either that or the Mazda dealer cocked up the gearbox oil change which was done at the last service back in April. Proving any of this for any come-back from Mazda will, of course, be pretty much impossible.

Do I have the only unreliable (petrol!) Mazda 6 in the country ?

Update - I've just received the car back and the jerkiness issue when accelerating and decelerating seems to have disappeared with the new gearbox and clutch.

Here are some photos of the old gearbox casing and diff which show what caused the failure :

http://s55.photobucket.com/albums/g136/mikej2005/Mazda%206%20gearbox/

It looks like that pin through the diff (should it be one pin ? if so, it's broken in two !) has been battering at the hole either side of the diff for the last 54k miles and almost made it a figure of eight, then it's sheared and blasted a hole in the gearbox casing which obviously then caused the leak. Does that sound right/plausible ?

I think a letter to Mazda is in order ! Hopefully the fact that this looks to have been caused by a fault they failed to rectify under warranty will help my case.