Hello Simon and Welcome..My name is XXXXX XXXXX Im happy to help you ..The issue with this is not usually with the gear selector - but it can be caused by any one of several other issues - from a fault in the actual transmission - back to the command... the computer module that has overall control of the system. Basically you have a basic transmission but the Tiptronic systems are electronically controlled.You can have a situation where the transmission has a mechanical issue / fault which causes this to happen...its rare to be honest but can happen but generally with an issue like this you should have a plug in diagnostic machine connected that will connect through to the computer module as above ( for the trans system ) and then that will ID the faults for you that way... then whatever is identified can be addressed.Other than doing as you have and checking wiring / connections etc to the trans, you really cannot ID / trace the faults on this any other way - SO thats the way forward on this one. The computer test will give out fault codes generally, it will also say what those codes relate to -thus, what needs repair / attention. Just a tip -ensure when you ask a local garage to do this test for you that they do have the correct equipment to connect to the Tiptronic system... many a mistake is made in connecting to the engine management system computer..where of course no faults would be found ! its a common mistake so I mention it so that you are best double checking when arranging to have this done.Let me know how you get on or if you then need anything else.Do let me know if you need anything else at all Simon..Kind Rgds - MIKE....Meantime..............Please do click on the "OK/ Excellent ratings" for me as that's how Im credited for helping you - Thank you in advance for that...You can and are most welcome to get back to me anytime you might need - clicking the OK ratings does not close you out at all..Rgds, MIKE.