If there is an intermittent problem, you should be able to find this by just wiggling the wires and bulb assembly while the blinker is on.
However, low voltage assemblies like turn signals are known to develop resistance on the connections that make the car diagnostics think the bulb is bad. I had a rear turn signal on my 325is that plagued me for 8 of the 10 years I owned it. The entire assembly was replaced under warrantee as well as numerous replacement bulbs until I figured out it was just a simple matter of schmutz that needed to be cleaned off occasionally. It is probably part carbon and part other stuff that builds up over time, but it is probably not a bad assembly.
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- Kenner
2005 X5 3.0 - K'Beige
Sport, Premium, Lights, Mirrors, R'Climate...
Mods - Aux Kit & XM Radio