Optimus does indeed not notice, and probably would not have even if he was able to see it. He has a slight blind spot, you see...

He tilts his head at what Shotlock says, one of his finials going down as he considers this. Is that a basis for weapons upgrades? Primes leaving random crystals that attached themselves to sparks?

"Try that one near the back," he says, pointing. "And... please don't start on the highest setting. If you aren't truly sure of the capabilities of this crystal..."