I have two with soft closers neither have adjustment,
haven't found one that has. I think they work on the principle of 'sucking in' air on lifting and expelling slowly (soft close) wait it might right itself mine did.
You could try what I did and squirt a small amount of silicone spray (I used polish with silicone in it) not too much just a smudging or even wd40 the spray with air freshener to take away the smell of the wd40. However, if its really an old one bin it buy another.
Bob UK, August 2014
