Faulty Lens ? AF stopped working ! [Canon 40D, 18-55 IS]

[driver8]

Well, this is a pain - looks like the AF on my Canon 18-55 IS lens has stopped working (and just before PAD2009 ! ) I'm posting to ensure I've not missed anything - tried a few things, and googled for other answers.

History
- I got the 40D with the cheaper kit lens about 18m ago, then soon added a 50mm/f1.8 (+ generic battery). Taken 4400 pics in this time, about 75% with the zoom.
- A month ago, whilst in the field, the AF stopped on my 18-55. I swapped to my 50mm which worked fine. This happened 2 or 3 other times in the following weeks, and I assumed it was a problem with dirty contacts. Cleaned contacts, all seemed OK. Looks like an intermittent fault.
- Yesterday, problem re-occurred, and I now cannot get the AF to work at all on the 18-55. Re-cleaned contacts, swapped lenses several times, 50mm works fine.
- all kit has been very well looked after, and not been dropped or knocked. Kept in case when not in use.

Symptoms
- affects only the 18-55, the 50mm is OK.
- turning the camera on with the 18-55 attached, the auto-exposure meter works fine, but the camera makes no attempt to focus, and the focus points do not illuminate. Cannot take shot as the camera 'knows' the focus is out.
- switching to MF, I focus manually (focus point illuminates accordingly & I get the BEEP, with half-press of shutter button) and take shot. I can use normally in MF mode. Swapping back to AF, if the subject is still in focus, I get the point illuminated & the beep, and shot taken. If I then reframe, AF seems to work but for one time only - I hear the motor, subject comes into focus, I get the illumination/beep, shot taken. Subsequent shots do not re-focus or take (unless I reframe on a subject the same distance away).
- it is as if the lens has switched from AF back to MF, but the scenario above (AF can take a single photo just fine) is repeatable many times, so does this suggest a software issue ? Could the AF/MF button be faulty or dirty somehow ? (I have rarely used the MF/AF button).

Troubleshooting - none of these have worked
- used centre focus point, and all points
- used ONE SHOT / AI SERVO / AI FOCUS drive modes, plus fully auto 'green box' mode
- cleaned contacts (small brass 'buttons' below mirror on body edge, plus corresponding on lens)
- turned IS on/off and AF on/off
- switched camera on & off, swapped lenses, swapped (fully charged) batteries
- reset all custom functions - both the "Clear All Custom Settings" and the "Clear All Custom Func"
- updated firmware (from 1.0.3 to 1.1.1)

Phew, sorry for the detail overload - tried to describe the scenario in full.

So, anything else I can try ? Is the AF on the lens now borked ? TIA

[RobDickinson]

Cleaned the contacts (unlikely) could be the switch bust, or the af motor.

[driver8]

thanks, Rob.

Looks like I'll need to get a repair quote ... lens is hardly used too, really ... pah