Okay, so I eventually got around to changing these. I bought German aftermarket boots and although its a little tricky measuring rubber with a vernier gauge I figured they were about 10% (0.3mm) thicker than the originals at the skirt. The component includes the top rubber mount on which the spring is seated so it does more than just keep the dust away from those precious (oh so precious) suspension struts (just ask your dealer how much they cost - but sit down first!). The indentation in the upper rubber mount suggested to me that a combination of potholes and speed-bumps have taken their toll over about 6 years. There doesn't appear to be any aftermarket shocks available which might be because the originals are very good.
Removal from the car was easy enough - penetrating fluid, wire brush, long leavers are your friends. Once out I found the compression of the spring needs to be way more than the 5mm the Mitsi workshop manual suggests. This maybe because in a workshop spring compressor it can be momentarily compressed perhaps 70mm in order to undo the top nut. I used a deep-offset ring spanner (17mm) to reach into the top of the strut housing. *Extreme care must be taken to avoid the top bearing being ejected into your windows or face * if you haven't compressed the spring enough! If I had a friendly garage nearby I would have removed the strut and taken it to them to compress, replace the boot and re-tighten the top nut - not even two minutes work. As it was I compressed it man-drolically - a good workout! I had to compress it further to refit as the thread was a good few mm below the bearing housing with the new rubber component in place.
I think I can detect a quieter improved ride from the front suspension now. Conclusion: doable, hard graft with only a DIY compressor and no power tools.
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