Turns out my 2002 R50 Cooper ran out of transmission fluid even though I took it into my local shop recently and asked them to check all fluids... as a result my tranny is DEAD and, apparently, the 5-speeds are much more expensive than 6-speeds...
So here's the question - can I put a 6-speed trans in a base Cooper?
I'm without wheels right now so would really like to know...

 

Yes, but it's a lot of work. Need new shifter box, shift cables, clutch line, flywheel,
clutch, axles, trans mount, starter, etc. (actually quite a few little etc.'s)

 

Yes, some good info here. It'll be a bit easier since you already have the 5-speed manual.