Perhaps it is already too old. Perhaps it couldn't withstand being opened up to 120°, sometimes up to 5 times per day. My DIY door closer quick and dirty repair only lasted 9 months. I had a final look at it and concluded that it is really beyond repair this time. There is nothing more that I can do to revive it. The only thing I could do now is to get a new one.
So, I went online and bought a new one from Lazada Malaysia. Looks nothing like the old one but it is functional. Installation is easy. It is just a matter of drilling the necessary holes on the door frame and later attaching it with the provided screws. Tension on the new door closer is adjustable (hex key is included in the package) but I find this unnecessary.
