It’s been my experience that the double-click problem is caused by the contacts in the microswitch getting dirty/oxidized. Usually, cleaning them will fix the problem for a while, maybe a few months, before it inevitably happens again. Supposedly this happens more frequently with cheap microswitches from China than with better quality ones from Japan, but I don’t have enough personal experience to say whether this is true. I do know that the area that actually makes contact is smaller than the head of a pin, so it doesn’t take much to make that connection unreliable. Typically, as well as accidentally double-clicking, you’ll see the left button randomly ‘let go’ while you’re dragging something.
Most mice use microswitches that look like this;
[image|2446328]
You can pop them open by inserting the tip of a knife into the edge of that little latch between the two holes and gently prying it off the catch. Then do the same to the other side. Be careful not to lose the ''TINY'' button! Some microswitches have the catches on the ends, but the principle is the same. Inside you will find contacts that look like this;
[image|2446329]
You can use some contact cleaner spray and gently run a pipe cleaner between the business end of the contacts (left side of the above photo). You can also try a sliver of fine sandpaper, folded double to scrub the upper and lower contacts at the same time. Note that the switch only uses the lower contact and the underside side of the movable plate. Technically the little arm that acts as a stopper is also a contact, but mice don’t use it, so that has no effect on the double-click problem. Half the time, the pin for that contact isn’t even soldered.
If this doesn’t cure the problem, you may need to remove the contact plate and clean the parts where it attaches to the base. Getting it out is as easy as ''GENTLY'' pulling the moving end to the side until the whole thing comes loose. Getting it back in is another matter. It’s a royal PITA! I find it best to hook the back end in the little notch and hold it in place with your finger, then use a pair of fine-pointed tweezers to ''GENTLY'' push up on the center spring while pushing down on the contact end. This will slide it into place, but the curved spring portion will be above the part that it hooks onto. You then ''GENTLY'' push down in the center of the spring until it snaps into place. Press down on the back of the plate, just behind the spring, about where the tool is in the photo, and check that it clicks down and back up again. If not, it’s not in correctly and you’ll need to do it again.
To put the top of the case back on without losing the little button, hold the top upside down and lower the board with the bottom of the microswitch onto it. Note that the button should be ''away'' from the end that moves. In other words, in the second photo, the button would go towards the ''right''.
On the other hand, you can de-solder the existing microswitch and solder in a new one. You can get them pretty cheaply on eBay, but then again, you may end up with cheap ones that will just end up having the same problem. If you do this, make sure that you orient the new switch in the same direction as the old one.
As for disassembling the R.A.T. 5, I found this video;
https://www.youtube.com/watch?v=sGRpQxCzuSE
Unfortunately there are no other parts, however as far as I can see, the rest of the disassembly is the same as for the R.A.T. 7, which you can see here;
https://www.youtube.com/watch?v=-XLzHzRB514
The main thing to be careful of is the small ribbon cable from the mode switch. ''DO NOT'' just pull it out! The connector it fits into has plastic tabs on each side which you ''gently'' pry up. They only move a millimeter or so, but that’s enough to release the cable. It should come out freely. To re-attach it, you insert it back into the slot and then push the plastic piece down to lock it into place.
The rest of the disassembly is just disconnecting the two cables to the board (one from the cord and one from the side buttons), taking out the three screws and then you can lift the board out.
Reverse the process to put it back together.