I was reading that water cooled 911's engine coolant tank leaks are a problem. I got thinking about how that tank is normally serviced per Porsche's own written procedures. To purge all the air out of the coolant system when the coolant is serviced or replaced, the system gets a pump attached to the coolant tank creating a lot of external pressure on the plastic tank (and hoses) as it pulls a vacuum on the system. The outside air pressure tries to collapse the tank and hoses because of the pressure difference. We have all seen those collapsed radiator hoses before on other cars. And if the tank is aged from heat and time, it is probably already weakened. It has me thinking the service procedure is part of why the tank develops cracks.