This preprint (Paper LXV) presents a combined statistical analysis of the S_8 tension across six independent cosmological datasets (KiDS, DES, HSC, Planck, DESI, and BOSS/SDSS). It demonstrates that the observed suppression of matter clustering is a consistent detection of gravitational slip, \eta(z) < 1, as predicted by the MSDS structured vacuum framework. With all physical parameters fixed a priori—specifically the vacuum offset v^2 = 0.00017—the model achieves a combined significance exceeding the 5\sigma discovery threshold without any post-hoc fitting