iPhone 4 not working in docks/car stereo anymore...

Hi guys,

I've done a lot of searching and it seems I'm not along with this issue, although none of the previous solutions have worked for me.

My iPhone 4 (os6) has recently stopped working with docks - in that, it'll charge but now allow any music playack, all of a sudden

This is a major problem for me as it also means it no longer works in conjunction with my car stereo!

So far I have;
-: cleaned the dock connector on the iPhone and on the car lead
-: tried different iPhones in my car (with the same setup - 4 + os6) in my car and they work fine
-: tried resetting and restoring my iPhone from backup, twice
-: tried the iPhone in different docks at home with no luck

Any idea why this is happening? Any suggestions?