Scirocco Central

Got light on the dashboard on about right tail light fault. When I found it, bulb looked ok, so I just clean touch points and fit it back. Ok for 3 days and light came on again. This time I changed the bulb. Today started car, after about 2 miles light on the dashboard is on again. Need to say that this light never come on straight away , but always after few miles from starting the car.
Any suggestions?

Could perhaps be vibration loosening the bulb if the holder has been distorted or the wiring connectors to the lamp unit. Not likely to be the earth if other lights function correctly.

Checked everything again, tightened all connection ( bulb-base and base- wiring plug) and we will see in next few days.
thanks for your suggestions