Here is my solution for keeping the stock spindle cool, I bolted up initially a 12V 40mm fan to the top cover blowing air down into the spindle and have since upgraded to a 24V fan that is hooked up in parallel with the spindle motor.
Initial tests with my crude temp sensor (my fingers) shows a significant temperature drop over the stock spindle with no fan. I am hoping this will keep my spindle running for a long time to come. I rarely do any heavy duty cutting since most is balsa and bass wood for now so she should last.
Also in the picture is my simple dust extraction system using a single loc-line and a mount cut from an old cutting board. I smoothed the pvc coupling in my lathe so I could use the bracket as a way of raising or lowering it.
The pic shows my initial tests with a 3cell lipo battery powering the fan