Use exactly what the manufacture recommends and nothing else.
If it is a CVT transmission then yes you can use cvt gearbox oil in a mini cooper.
unleaded
Use exactly the weight that Mini recommends. http://www.ehow.com/list_7739452_list-mini-cooper-approved-oil.html
The manufacturer recommends that you use 10W-30 motor oil in your 2006 Mini Cooper. Use in extreme climates may call for a heavier oil, like 10 W40.
yes, i use royal purple.
Consult your owner's manual.
You probably have a leaking oil seal or cylinder head gasket.
Wrong oil filter. Must use OEM oil filter in Mini's. The aftermarket filters dont have the proper check valve inside.
I use about 4.25 qt (about 4 L)
The 2009 MINI Cooper runs on premium unleaded (required).
The 2011 MINI Cooper runs on premium unleaded (required).
The 2004 MINI Cooper runs on premium unleaded (required).