The incident happened when a woman in her 40s was walking her dog in Ruislip Woods, near Wiltshire Lane at 6.40pm on July 21.
She was approached by a man wearing nothing but a white t-shirt, who then indecently exposed himself before leaving the scene.
The police have now released an e-fit of a man they wish to speak to in connection with the incident.
Detective Constable James Scarr, from the Western Area Local Investigations team, said: "This incident took place early on a Monday evening, not far from a residential area.
"Months have elapsed, and we have explored most lines of enquiry in this case – with limited forensic and CCTV opportunities available.
"We have taken the decision to release an e-fit of a man we wish to speak to in connection with the investigation.
"Do you recogn

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