NEVER use WD-40 in an EM machine. WD-40 is not a lubricant or cleaner, it gums up over and time and worst of all is highly flammable. A spark might set off some of the residue left over and start a fire.

If there's a lot of grim my go to is 99% isopropyl alcohol and a lot of cotten swabs. Just MAKE SURE it's at LEAST 92%. I find anything lower leaves a white residue behind that can cause electrical havoc. If you do use it, make sure the area is well ventilated and wait at least 15-30 minutes after use before turning the machine back on. While I've never personally had issues even after 5 minutes, better safe then sorry.

While you generally don't want to lubricate anything, if need be the only thing you should use If Teflon Super Lube Synthetic Grease. https://www.amazon.ca/Super-Lube-21030-Synthetic-Grease/dp/B000XBH9HI
And if you do, only apple a little to the rivets at the back of the ballcount unit so the plate travels more smoothly. Don't use it on the shaft or anything. Stuff works well, it was able to get a stiff gottlieb AS stepper working again and saved me the headache of trying to take it apart.