I'll add something else to the pot that has not been discussed. We've been debating to no end the life of fluid etc., but has anyone considered the life of the filter?

I don't know the specific design of the ZF filter in question, but on many cars, the filter has a very similar design to the engine oil filter in that it is designed for bypass flow conditions. In other words, to maintain flow when the fluid is cold, the fluid is not filtered and goes through the bypass valve, until the fluid is at operating temp. and then it is filtered normally.

After 100k+ miles on the original fluid and filter, the filter may be choked with metal and clutch material to the extent that to maintain fluid pressure, the transmission operates in 100% bypass mode. This would mean that unfiltered fluid with metal particles and clutch material would be circulating and building up in the valve body and other sensistive components causing accelerated wear.

My advise… if the tranny is not giving you any problems ... Don't touch it.

I would agree at high mileage, if regular service has not been performed, it's better to save money for a new car or for a new tranny. Often the only thing keeping the torque converter from slipping is the added friction from the suspended metal particles in the old fluid.