This is not about cv boot directly, but about the little accordian shaped rubber (I have another name for it too but can't say it here) expansion boot found on the front and rear gearbox areas.
I had always assumed this flex tuber expands and contracts with the temp. of the gear oil, avoiding a traditional breather cap that may allow water into the system.
One extreamly hot day I was riding hard and took the road back to my camp. When I got there, I noticed a few spots of oil on the rear end. It was the Thingie had split at one of the creases. I think it was from the heat. I cleaned it well with rubbing alcohol and then put permatex bonding glue (they make several, don't know which one) that is good for rubber, so it said on the label, and glued the split. I let it dry several hours, then wraped it in adhesive (the white fabric medical tape)tape. This tape is the older medical tape that sticks well to your body and leaves sticky crap on yr skin after removing it. Anyway, that was about two years and 2,000 miles ago. Been through everything I can think of including deep water for several minutes at times. Would you believe, this still holds! The tape is still white! I check it often and I even ordered an extra thingie for replacement. I changed gear oil twice since and no sign of any water. I really should change that thingie. This was to be an emergency repair as I was at my remote camp. It still flexes and is in good working condition.
Another thing I do is spray PB Blaster on my boots (only on one machine for now) and it keeps the rubber softer and flexible. PB Blaster is kinda like WD-40, but more toward lubricant. The PB company said it's the best thing to use on "O" rings. I give all my o-rings a shot and it keeps them like new. But don't know if this is good or bad until a few years from now.
Sorry for getting off topic, but I found it interesting and well............sorry to be off topic!