This article presents and validates a 3D-printed fully metallic sub-THz leaky-wave antenna (LWA) based on a glide-symmetric spoof surface plasmon polariton (SSPP) transmission line. A high scanning rate is enabled by the glide symmetry in the transmission line that increases dispersion. Asymmetric periodic modulation excites leaky-wave radiation and suppresses the open stopband effect without extra elements. A gap waveguide (GWG) in the feeding structure mitigates potential energy leakage from assembly gaps and simplifies assembly. Experimental measurements demonstrate continuous beam scanning from -29° to +49° from 180 to 220 GHz with a 3.9°/%BW scanning rate. Peak gain varies between 11.13 and 16.53 dBi.