I recently bought a used switch from eBay which didn't come with Joy-Cons as a gift for someone else. Took my OLED's Joy-Cons and popped them on to test while I was waiting for the new Joy-Cons to arrive...

Well little did I know there was something sticky that had gotten on the contacts of this used switch, which then transferred to the Joy-Cons. I of course plugged them back into my OLED trying to figure out what was going on and transferred enough of whatever it was to my OLED to start causing problems as well.

Long story short it doesn't take much to break that contact.

If you have an original switch and the right tools to open it up (needs a tri-wing screw driver), it is pretty easy to open it up, remove the contacts from the rail and thoroughly clean them. Worked perfectly to get the used switch back to brand new.

Of course don't forget to do the same on the contacts of the Joy-Cons They need the same tri-wing screwdriver to open.

The OLED is a bit more of a PITA to get the rails out, so if you have an OLED or don't have the tools to open your original you can make a makeshift cleaner like this person did (sorry about the reddit link). Joy-Con Rail Contact Cleaning Tool

I used a much smaller cable tie so that I could fit some isopropyl dipped gauze around the tip to get into the contacts (power off your switch entirely first!!!).

Careful on the Joy-Cons if you try to use something like that tool. The Joy-Cons are the spring side of the contact so you could easily bend them and make things worse.

If you have problems with stick drift and feel comfortable opening them up, you can get replacement sticks on eBay for $5-6 a piece.