Nope it came with it. This was back in 2015. Still have the same body in storage.
My slash also came with OBA. The speakers got some water in them and stoped working and I have no idea where the module is.
And I raced my slash in the 2wd SCT young guns class back in 2016. That was pretty fun...
Traxxas Slash xl5 brushed. Got it for Christmas 2015. Next RC was a Rustler xl5. Got the rustler in 2020. Then my latest car is a losi mini. Got it this April.