Good news! That's what the forum is here for.
First, your pump may last; is there water coming from the telltale hole?
Second, here is a list of the obvious things:
Before ordering the pump, read this post:
http://www.sl113.org/forums/index.php?topic=8820.0 There are 3 different pumps. Obviously you need the right one!
Then read this one (it'll reassure you)
http://www.sl113.org/forums/index.php?topic=8756.0The job itself is very easy, actually. You can drop the radiator and do it, but if on the road you may be better off undoing one side of the bonnet and lifting that off (having marked the position of the fastenings so it goes back on in the same place - you can always tinker with it later to get it right). It is more easily done by removing the radiator, and that isn't a hard job either. Note that you can loosen the rad and it will slide forward to give you a little room to work (less easy if you have a shroud).
If you wanted to enjoy your trip and leave it to a shop, any garage could do the job in an hour or two.
If you're going to remove the rad, I'd strongly recommend you/ the garage drain it using the lower drain hose and NOT the drain plug at the bottom of the radiator. Here's why:
http://www.sl113.org/forums/index.php?topic=7663.0Finally, if you're going to put in an order for the pump, you may want to change the little pipe shown in the photos.
If you have any more questions, shout.
JH