i have a late 2003 cooper with 38,000 miles and generally it has been fine.
however the old rover sourced gearboxes (prefacelift One/Cooper models ie before July 04) are prone to going. mine went after a trip to the Ring at around 23,000 miles. New one has been fine but bear that in mind as if its out of warrenty its an expensive repair. postfacelift models on these use a Getrag box which i believe to be far more reliable and the One D and MCS used this from day 1.
apart from this and the odd rattle etc. its been great
