Key won't stay in the slot?

[SattyA4]

Hi All, My 2008 A4 has a funny issue where the key doesn't stay in the slot. I can start the car the usual way by just pushing the key in, but once the car is started the key can simple just fall out. Don't need to keep the key in the slot to keep the car running either?! Its a bit like having keyless go. Any ideas what it could be, Thanks

[dufferum]

There is a small indent along each side of the fob, I've experienced a gradual build-up of dirt in these enough for
Key not to locate, simply cleaning them sorted it out