I tried dismantling one. The rivits just hold the plates together and the rubber is impossible to remove without destroying it. Might be possible with a press but how you get it back together is another matter.
After my original post,I too have tried to dismantle the top mount.
As it was just slightly notchy I tried beforehand to lubricate bearing from top in the space between centre bearing and angled bit which the rubber cap sits over.
This made things better but still slightly notchy, but when I got the bearing exposed after splitting plates
it was nicely oily and would have outlasted me.
Although bearing has integral dust covers, I wonder if water from a split rubber cap had got in.
Fitting rubber caps seems essential.
When I measured the rh and LH ones, I came to the conclusion that they are not interchangeable.
I have kept old ones in case for template.
It may be possible to MIG ends of good RH ones on to LH ??