VTC16B Thru Coolant Issue?

I have a ~20 year old VTC-16B that during the tooling changeover pukes coolant through the spindle. At least a cup at a time, even though thru coolant is turned off at the beginning of every shift. I feel like there is an easy answer to this, but I can't seem to find anything online about it. Any ideas would be greatly appreciated.

I don't know about Mazaks, but I had this same issue on my Mighty and this was the issue:

There is a CoolJet tower behind my machine that supplies the high pressure coolant. The system works by using the flood coolant pump to draw coolant into the high pressure pump, which then pressurizes it to 1,000 PSI and pumps it up into and through the rotary coupling down through the spindle. There is a solenoid valve on either side of the flood coolant pump - one valve opens when the flood M code is activated and is plumbed to the flood coolant nozzles. The other valve opens when actuated by the high-pressure M code. This is what allows the low-pressure pump to move coolant into the high-pressure. If your solenoid valve running to the high-pressure pump is staying open, you will get low pressure coolant pumped through both solenoid valves when the flood coolant is turned on. The coolant has enough pressure to move through the high-pressure system, which is why it dumps out the spindle during the tool change/air purge.

Like I said, my mill is not a Mazak but hopefully this helps you solve your issue.