hmmmmmm reading that item, I can't imagine at the moment how you would GET AT that sleeve. It seems to me that it would be 'hidden from view/access' by the bracket on the bottom control arm...
But, in case I am making that up, the 'sleeve is the small steel 'tube' in the bottom shock mount. There is the large diameter piece of tube that is the 'whole' lower mount, and inside that is a rubber bushing (permanent) and then inside that rubber bushing is the sleeve. Probably (guessing) about an 8 or 10mm dia (not HEAD size) bolt. That sleeve is the thing they are talking about. It is not actually tube, just a flat piece of metal that is rolled up to form a 'tube' around the lower bolt. So where the rolled ends come together it forms a seam. I haven't seen a conventional shock that doesn't do that.
The article you mention talks about putting QUITE a bit of torque on a wrench to twist the bolt against the shear strength of the rubber bushing in order to 'find' the seam in that tube. I am not sure how you would see it or get at it, assuming you can do that in a controlled fashion, but yes, be CAREful. I expect that wrench will want to 'return to point zero with a lot of determination.
I don't remember having particular difficulty with mine so can't offer any help. ONE thing to always keep in mind, tho, if you are hammering something - ANYthing, with the hopes of removing it,
MAKE SURE THE THING YOU ARE HITTING IS NOT MOVING OR ABLE TO 'SHAKE' OR 'VIBRATE'... that way the full force of the blow will go to 'loosening' the bolt or whatever, and not be wasted in simply making the item shake around a bit. Things like control arm bushings absorb road bumps and car weight - size forces. A hammer blow is peanuts, they will just shake a bit and nothing will be gained. So firmly block the item so that it is very very solid and then do the hammer thing.
Anyway, if you DO try it and it DOES work, let us all know! And good luck.