Well... The oil pressure light was "dim" on my impreza for 2 weeks in September (usually afternoon, not in morning, temperature is 20c). The service maintenance done in August and the oil level is above full mark.
I've tried to turn off the engine but it doesn't go away.... Did some research and check the repair manual.... I assume its related to the wiring/electric/grounding issue or something related to the oil pressure sensing unit
Luckily it no longer comes up now. I will bring this up again if I see it next time to the technician.
Just a record for anyone who may have the oil pressure light (dim) in the future.