spindle through coolant use for cutting tools which is having through hole. Through coolant help in cutting chips removal, cooling of tools etc. In case of through coolant pressure drop, tools fail prematurely.
Through coolant pass through drawbar, where pusher stick with tools pull stud. Here due to pusher rubber damage, coolant leak from spindle taper which is going to drawbar , reducing through coolant pressure.

for more clarity on drawbar please watch my video on drawbar assembly #mechanical #assembly #drawing