DJM 250 loose knobs ?

Hi folks,

I just bought a used djm 250 rarely used and in a brand new condition. However i notice that all the knobs have a small "dead play" ( not sure if it's the correct term, english isn't my native language ). So they are are moving a little bit when i grab them and shake them a bit. They actually do all this and especially the left big filter knob which is even more pronounciated than all others and the right filter knob. It feels very awkward to me since i always hear that those mixers where solid and well built...

Is this thing particular to the Pioneer mixers ? or is there anyway to tight them ? It's my first Pioneer mixer and before i had a other brand mixer which had no issue like that and the knobs where firm and tight.

Thanks for reading