Hi Barry, I am an AK right too, and coming up for my 18th anniversary, I have experienced the numbness at the end also, I always put in down the the fact I use suction, and at times, just sort of sucks at a different place and leaves the end numb. I wouldn't worry too much, but if you are worried just pop along to your GP, but I'm fairly sure its all to do with the nerves and the pressure on these. (we can't get our legs on exactly the same place all the time).
Hope it turns out OK