How do you replace the manual shifter boot in a w123? Mine is all crumbly and has huge holes in it

I know, it is probably really simple to do, but I don't see how it is attached.

Is there any potential problems that may have been caused by it being open? I found a bottle cap in there when I was cleaning the car out Should I do anything to clean it while I am replacing the boot, other than just picking out any other obvious debris I find?

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