Yesterday I was doing an overall check on bike and notice the headset was loose - I kind of remember having it wobbling some days ago.
I notice some grease had come out - so I guess I was riding for a good couple of days on this condition.
Didn't notice since I carry a lock cable there.

Is that common the headset to get loose?
I have some washers that can contribute to it, but I only have some 1000 miles on it after it was put together.

it is not common for headsets to get loose.

You need a headset wrench , they're 1/8" thick... and for the locknut a big adjustable wrench will do..

If you get the lock nut tight it should not get loose..,

you hold the bearing adjustment with the headset wrench..

As [MENTION=197614]fietsbob[/MENTION] noted above, you should be able to tighten the adjustment and lock it in place.

N.B. if it doesn't hold adjustment after that, it may be that the threads on the steer tube are damaged from riding too long with loose adjustment. Take the threaded pieces off the steer tube, remove the fork from the frame, and inspect the threads for damage.