Speaking from 1st hand experience also, with exactly the same prob. I found that the surround plastic trim under the leather had broken.
I posted same subject some time ago here:
Broken Gear Lever Shroud Base.
The supa glue repair has not lasted however. weasel's option sounds good although my problem remains with the plastic base/surround. Have learnt to live with this shitty little problem for the moment, probably saving some fuel by not thumping it in manual.
Gear lever top piece (in leather) is fairly tight on the shaft, it will come off with a good steady pull and simply clicks straight back on, just don't give yourself a black eye in the process
GL