Thanks you all for your advice. The verdict is out.
The stray hairlines on the picture was due to fungus.
However the fungus cannot be easily cleaned. They have to open-up my camera.
(yes, not just remove the lense only but open-up the body.)
Due to something like the fungus is between the low pass filter and sensor.
Luckily it is a recent growth ( about 2 months), so just clean it is enough. No lasting damage. No need to replace filter nor sensor. Thanks goodness!
For those keen to know, the service charge to open-up and clean, is $120+GST.
Err... $120.. not too expansive lah, because you actually need not replace the sensor. On the other hand, not so cheap also for a servicing.
Just to share my experience with drybox. I put 2 "hippo" packs inside my dry box. The humidity meter ( if no hippo , will be at about 70 ) will go down to about 40~50.
Careful not to "over dry" the equipments, I heard that the lubricating oil will start to dry up if the environment is too dry. If too humid, fungus will grow... haiz...
I checked my hygrometer on the dry box. It is showing just before 45%, so say 44%.
(When I open, it goes to above 55%, so confirmed meter working....)
Now scared lio. Will check the meter reading now and then.
I don't use hippo. I used silica gel, many packs.