Aerosmith is ready to bring their original drummer back into the fold -- Joey Kramer's set to take the stage with his bandmates, and even crazier ... NO AUDITION NECESSARY!

Sources with direct knowledge tell TMZ ... Joey's being brought on to play drums Monday night with Steven Tyler, Joe Perry and the rest of the fellas for a performance at the Park Theater in Vegas, which is where their residency shows are currently being held.

We're told the band didn't wanna jerk Joey around -- they're bringing him back without holding another audition, and it's because they feel he's probably up to snuff and in good health again. Plus, our sources tell us it's an act of good faith between old pals.

You'll recall ... things were getting pretty ugly between Joey and the guys just a few short weeks ago ahead of their Grammys performance, which Joey was fighting tooth and nail to be a part of -- even taking the issue to court in a last-ditch effort, but was unsuccessful.

Hell, they even turned him away at the door when Joey showed up unannounced for a rehearsal ... so yeah, the tension's been high between these guys.

Part of the reason Aerosmith didn't feel comfortable reuniting ... Joey hadn't played in at least 6 months, and they didn't wanna risk a shaky gig with a guy who was rusty/lacked energy. They put him through the wringer with a live audition but felt he wasn't ready.

Now, it seems they've had a change of heart and are prepared to embrace an OG. Should make for a great show ... stay tuned.