How does one know if a FBT has ever been replaced in any given RCA? There really is no way to know, is there, w/o knowing the history of the set. You can make a guess by looking, but never know for sure.
I have 2 examples here, Rocket's CTC-16XL and Freakaftr8's CTC-16.
I will look at mine closer this weekend.
I suspect that Freakaftr8's is original and Rocket's a replacement.
Reasons...
Freakaftr8's , Darkened metal at base, same as chassis, doughnut color darkened, wires held with black tape ( common with oem )
Rocket's , metal at base much lighter than chassis, doughnut color cleaner looking, no black tape seen.
https://imgur.com/d4cpPzR
https://imgur.com/W4JoHPn