I found the Centric 143.10000 is a good kit. Rubber parts made in UK. Good fit. Comes with the round clips, but the groove will accept the stock flat narrow retainer ring. No boot slippage. On eBay at about $10 per side.
Still required is a 9/16 OD, 7/16 ID (1/16" section) brake fluid friendly O-ring to seal the e-brake actuator bit inside the indirect piston.
Replacement pistons were a bit of a chore to find. The other internal bits seem to be unobtainium.