If you haven't had these out for a while, it's usually a good idea to throw a new cup-and-ball (also known as a knuckle joint, among other things) on there. There's a nylon cup which sits in the top arm at the front, and in the trailing arm at the back, which the rubber seal on the ball should've been hooked over. The cup is usually filled with grease, hence the rubber seal. If you can't see the lip of the nylon cup, it's a very good idea to dig the remnants of the cups out and replace them! The ball will last a good while, but the cup will wear faster. They're not too dear, and it means you can forget about your springs/hilos for a while.

If you've got the hilos back in there, still look, having hilos in there makes it easier to get your springs out without using a compressor. They often sell the knuckle joint with hilos, but not always.
Just make sure the person behind the desk knows what you're after. I went in and asked for the cup and ball joint at my local shop (not a Mini specialist), and they told me to come back in a week when they came in (and quoted me $200!). I went away, only to discover when I came back they had a complete set of upper and lower ball joints - the ball joints at the hub, not the knuckle (cup and ball) joint!

When the misunderstanding was cleared up, things were a lot cheaper.
