M32 history, from calling around European shops and checking out Vauxhall/Opel forums.
Unfortunately these transmissions arent common pre 2010 in the US. They've been used in Europe for a while on a few dozen different cars, their limits have been tested and are known.
When GM produced them for the US & world market in 2010, they got a new bearing contract (2010-2012) moved away from Timken to other brands which proved to be less durable. They also added the dual mass flywheel to prevent driveline shock from hard shifts, a way to manage torque... a nice unintended result of the dual mass flywheel is it dampens vibrations and lowers gearbox chatter in neutral. There are more problems with the 2012 Sonic 6 speeds than later years. They redesigned the case cover in 2011 so all Sonics should have the newer style which supplies oil more efficiently to the case bearings, but the bearings are less robust until 2013, the same year the shift tower was redesigned for more precise adjustment of the cables.
According to WG Motorworks, one of the leading aftermarket M32 rebuilders, reasons for failure are:
"poor gearbox design; oil temperatures which can exceed 115 degrees C, and failure to change the gearbox oil according to the service schedule."
Since the US M32's do not have an oil service schedule, and it is known the oil gets too hot even in stock applications 115-135 C (240-275 F), above the recommended operating temps of 75w90 or SAE50, it makes sense that so many people have shifting issues. Any ways that cool the trans or gear oil more efficiently will help, if they do more good than harm. Or we can do what the dealer does and throw away the old trans and buy a new one.