SPC's history
Version 1 - Rubber bushings, large washers on all sides (8 washers).
Version 2 - Poly bushings, large washers on all sides (8 washers). These are the ones that fail in high temp climates. The large washers "squeeze" the bushing to the point of collapse. This does not allow the control arm to pivot on the bushing. Effectively, making the control arm bend up and down at the welds.
Version 3 - Poly bushings, 4 large washers, 4 small (2 large washers on the outer most part of control arm, 2 small washers on the inside). This was SPC's solution to an extended sleeve. This does not allow the bushings to be completely compressed by large washers.
Version 4 - Poly bushings, 4 large washers (2 large washers on the outer most part of control arm). In this version the sleeve is longer and is completely butt up against the "tower tube".