2005 A/T question
 

Does anyone know if the 6 speed A/T in my cooper S can be made to stop hard shifting after it is warmed up. Is this something I must live with or can stuff be added to make it better

how about adding a drain plug to the pan and changing the fluid a bunch of times or adding an external cooler

Have you checked the fluid level? If the level is good it could be that the fluid in your transmission is breaking down once it warms up. A lot of MINI drivers actually like running Red Line transmission fluid. Have you ever replaced the fluid? We have a lot of great info about the fluid change for the 6 speed Agitronic transmission here: Pelican Technical Article: MINI Cooper - Automatic Transmission Fluid Change

Red Line fluid for your transmission is D4 ATF here: Pelican Parts.com - Red Line D4 Automatic Transmission Fluid and don't forget the filter here: http://www.pelicanparts.com/catalog/SuperCat/6319/MIN_6319_TRAUTO_pg1.htm#item3

Try that out and see if it makes a difference. Let me know what you find out.