You have to replace whole part, boot is not separate. Prolly discontinued but probably find new on eBay. I have a part number somewhere I'll have to...
I had to replace that in my MM 10ish years ago. Just went to Ford dealership to get a new one, then took car to local garage to have them install it....
Sorry for not posting sooner. It comes with needle and thread so you can DIY. I didn't do a very good job, which is why it looks like crap, lol. But...