Everything w0rks fine except the letter "0" 0n the keyb0ard ? Seri0usly! Any suggesti0ns. It can be intermittent but makes using passw0rds difficult. Thanks.
What model do you have if it is a recent one there has been some chat about keyboard issues - you may need to chat to a genius at an Apple Shop
It is a late 2011 model, running High Sierra 10.13.4 and with recently upgraded 8 gb RAM. Currently the oooooooooooo's are working. No other keyboard problems here except the intermittent o's.
Unless you have some kind of text phrase expander software or something else intercepting keyboard input and altering it, I'd say it's almost certainly a hardware glitch developing with the keyboard. Presumably no liquid spills on the keyboard?
No spillage issues. May just get one of those cans of pressurized air and give the keyboard a few good sweeps with that.
If you are near to an Apple shop telephone them and make an appointment for them to have a look at it - search for a local Mac repair chap.