Hey man
It is not the easiest thing to replace, and you will have to solder some.
You will take off the FRONT of the MPC, not the bottom.
I actually just did this repair myself last week, and so here are some pictures.
This is what you will see when you take the face plate off. You do this by undoing the screws on the SIDE of the MPC.
http://www.turntablearchives.com/mpc2kxl/?pic=9
Now some detail, you can see on the left I have the slider disconnected at the bottom and it is flipped up. Take note that you will also need to remove that metal thing that sits underneath it.
http://www.turntablearchives.com/mpc2kxl/?pic=16
http://www.turntablearchives.com/mpc2kxl/?pic=17
To do the actual repair, I did not disconnect the circuit board, but just flipped it on it's side. See this pic...
http://www.turntablearchives.com/mpc2kxl/?pic=19
If you want to do it like that, do it at your own risk. Gravity is not your friend at an angle like that. If you can, be careful about it and just take the whole circuit board off so you can lay it flat while you desolder and resolder the slider.
Hope this helps.
-J
ps. FWIW I used my MPC without the slider for years...not entirely necessary but fun if you got it.