I have repaired a grey Miele boot using grey roofing silicone sealant.
It was two similar small holes to the one shown in the first photo.
you need to thoroughly clean around the hole on both sides with something that doesn't leave a residue. Set the boot up in some improvised holder so that you can work on the repair without the other parts of the boot getting in the way. (like your foot is doing in the photo.)
Cover the hole from the side you will see in use with some of that easy-to-remove masking tape. (the blue stuff.)
On the back side cover the hole with the roofing silicone and smear it to make sure it is well bonded to the boot. Use disposable gloves to protect your hands.
You need a bit of judgement to get the thickness right. It needs to be thick enough to be strong but thin enough to stay flexible.
I placed a bit of baking paper over the repair till the silicone had set. The boot will want to flop back to its natural shape and the paper is to prevent the silicone bonding the folds of the boot to each other. This is important - if the folds are glued to each other, it won't be able to flex and will tear apart on a jumpy spin.
Leave it alone for 2 or 3 days to really set strongly. then carefully remove the baking paper, or if it is stuck, trim away excess paper but leave where it it stuck to the silicone.
Recognize that this is a temporary repair. The boot is worn. It might last a month, it might last a year. But it isn't long term unless you really can't get a replacement, then it will just have to do.
the repair I did is in a friend's machine that lives a hard life and it had held up about six months so far...
