+ 497992 \right)
C_A C_F T_F {N_{\!f}}+ \left( 570240 \zeta(3) - 244505 \right) C_F^3
\right. \nonumber \\
&& \left. ~~~~~~~~~~~~~+~ \left( 1036800 \zeta(3) - 814508 \right)
C_F^2 T_F {N_{\!f}}- 82208 C_F T_F^2 {N_{\!f}}^2 \right] a^3 ~+~ O(a^4) \nonumber \\
\gamma^{W_3}_{12}(a) &=& -~ \frac{3}{2} C_F a ~+~ \frac{1}{144} \left[
81 C_F^2 - 848 C_A C_F + 424 C_F T_F {N_{\!f}}\right] a^2 ~+~ O(a^3) ~, \nonumber \\
\gamma^{W_3}_{13}(a) &=& -~ \frac{1}{2} C_F a ~+~ \frac{1}{144} \left[
103 C_F^2 - 388 C_A C_F + 104 C_F T_F {N_{\!f}}\right] a^2 ~+~ O(a^3) ~, 
\nonumber \\
\gamma^{W_3}_{22}(a) &=& \frac{8}{3} C_F a ~+~ \frac{1}{27} \left[ 376 C_A C_F
- 112 C_F^2 - 128 C_F T_F {N_{\!f}}\right] a^2 \nonumber \\
&& +~ \frac{1}{243} \left[ \left( 5184 \zeta(3) + 20920 \right) C_A^2 C_F
- \left( 15552 \zeta(3) + 8528 \right) C_A C_F^2 \right. \nonumber \\
&& \left. ~~~~~~~~~~-~ \left( 10368 \zeta(3) + 6256 \right) C_A C_F T_F {N_{\!f}}+ \left( 10368 \zeta(3) - 560 \right) C_F^3 \right. \nonumber \\
&& \left. ~~~~~~~~~~+~ \left( 10368 \zeta(3) - 6824 \right) C_F^2 T_F {N_{\!f}}- 896 C_F T_F^2 {N_{\!f}}^2 \right] a^3 ~+~ O(a^4) ~, \nonumber \\
\gamma^{W_3}_{23}(a) &=& -~ \frac{4}{3} C_F a ~+~ \frac{1}{27}
\left[ 56 C_F^2 - 188 C_A C_F + 64 