There is no prior warning to when a transmission is about to milkshake and once it has occurred, it is extremely costly to fully rectify.
There are a few theories as to why they fail, yet none have been 100% proven.
Some blame lack of coolant, but we have seen them fail on cars that have had correct cooling system maintenance. Another theory is stray current or vibrations causing it to fail. We have not seen these problems either.
Some people are changing the factory heat exchanger as often as every 50,000 km’s to try to play it safe, we have seen one that had failed at 52,000 km’s so it’s still a little risky.
Another option some people go for is an air to oil cooler which means that it will never be able to get a milk shake as there is no coolant in the cooler that can cause an issue.
The problem with this is the transmission can run too cool and affect gearshifts and many coolers being used are actually too small internally and can restrict oil flow.