Driver side front blinker
 

It won't work.

The right side (front and back work great). When I signal left the rear left has a very fast blink... but the front won't go.

I confirmed the bulb is OK.

Fuse is fine..replaced it with the right and same symptoms.

Any idea where to search for a problem?

So many places, I guess you swapped the bulb from side to side? Any voltage at the lhs? Corrosion on the brass contacts, dodgy earth, corrosion on the alloy housing, problem connector into trunk area, could be anything.