Hi Tien,
Hope you are doing well.
The best way to reach the XO and L-pads is to lie the RM/x down and remove the Passive Radiator and Bottom Woofer.
They will likely be difficult to remove since the gaskets set up like glue over the years.
Remove ALL the screws and then take an OVERSIZED screw and force it (by screwing it) partially into one of the holes on the Woofer or PR.
When that screw feels firmly (but only partially) in the steel portion, take a pair of pliers and slowly and gently pull until the bond between the woofer or PR breaks free. Then you are all set.
Remove all the fiberfill and you should be able to access the XO and L-Pads.
You will probably need to gently "pry" the bad L-Pad off the board. It is Hot Glued to it.
MAKE SURE AND NOTE THE CONNECTIONS TO THE L-PAD! As well note the "orientation" because this will determine where 12:00 is
You should be able to tell which one it is, by how easily or how hard it turns. It will either have NO Resistance, or it could even be frozen.
You can tell by feeling the undamaged L-Pads.
Take a good look at ALL the other L-Pads to see if they are "discolored" by over-heating, which is what causes them to fail. And again, bad ones usually have a far different feeling when turning the shaft than the smooth feel of good ones.
Let me know if you need additional help.