Advice as previous.
However some shrink tube is glued on but still will peel off .
You can leave the old on and put new over the top.
You can get shrink tube off ebay, but I find it expensive, also ensure the length you purchase is long enough for what you want and the right diameter.
It has to be big enough unshrunk and small enough when shrunk.
A heat gun will shrink it down, start at one end, keep rotating the rod over the heat and work your way down the rod. You can use an electric hob holding the rod about 3" above and keep rotating until it shrinks.
Radio Spares and CPC also sell heat shrink and it can be a lot cheaper.