If you are talking about the CV boots I'd replace them both. Also look very closely at the joint. If it lost a lot of its grease & ingested a lot of dirt it may not be long for this world.
You have to remove the outer to do the inner anyway, so may as well do both. I just did this on both sides. A vice was essential and I needed a very large hammer and a couple of beers to get everything apart initially. If it's the driver's side, then the c-clips are a pain, but otherwise it's not too bad a job.
I've found the Inner boot kit for about $55.00-$75.00 using the MINI branded parts and I have found the Outer boot kit for the same price using the MINI brand parts as well, BUT I have found the Outer kit from GKN Loebro for $9.25 with all the same parts and grease - they are an OEM supplier. The Inner kit can be had from EMPI for $13.75, but they don't stock them.
