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Moisture/condensation in transmission/rust on dipstick

my daughter has a 2004 Buick Rainier V6 approx 50,000 miles. It upshifts and downshifts slightly hard enough that it is noticeable. Took to dealer and they could not find any codes in the on board comp. But did notice a shudder when driving. also that the dipstick had some rust on the tip and they needed to drop the pan cover and inspect for water /moisture and see if trans is damaged or need to replace other components ie solenoid etc.I had noticed this rust problem previously on the dipstick last july and pointed it out to the service writer and his comment was that GM had a problem with condensation on some models. Nothing was done at that time but it was noted in the service history. Now it seems that it is a problem. Fortunately they have assured me that they will take care of any repair 100% because of my being a good customer and that issue should have been addressed in july when the warranty was still in effect(powertrain). Has this been a problem with this model or GM in particular. I have other GM products and have never seen this.

I have seen plenty of transmission dipstick housings (the tube you put the dipstick in) rust but rust on the stick its self? it is sitting in oil.

Can anyone connect the dots here? condensation in fluid that doesn’t get “burned off” as the fluid heats up and then this condensation damages a control part of the trans,also in oil.

What makes one transmission more prone to having condensation (hope it’s not coolant in the trans fluid) over another?