The Mini's rear subframe is rubber mounted. Polyurethane (stiffer, much longer lasting) bushes are now available for the rear subframe trunions. Cars manufactured before 1976 used the same bush 2A5818(C-STR638) at the front and rear of the subframe, 8 per car.
The colour of these bushes are purple.
Starting in 1976 (MKIV) the front trunion bush was enlarged, that bush (21A2560) is now available in a harder format(C-STR639). These later cars use 4 of each 2A5818(C-STR638) and 2 of 21A2560(C-STR639).