Yes it was the sister car to the C 32 AMG, but was not available in all markets. Never officially available in the UK they’re a rare sight. I’ve seen four or five over the last 20 years but they’re always on foreign plates.
In the early 2000s there was some debate about the development, marketing, and sale of hot diesels, which focused on four options: (1) Factory AMG models with diesel engines; (2) Brabus kits which would be fitted at the dealership to standard diesel models and sold as hot prebuilt models: (3) Brabus tuning options would be available from the parts counter in all dealerships without affecting warranty; or (4) Just sell them as Mercedes.
The C 30 CDi was dipping a toe in the water (option 1) and Brabus accessories (including the PowerXtra tuning box) were available to order from all main dealerships in the mid-late noughties. Neither really took off though, and the few Brabus diesel models were from the small handful of Brabus dealers, most of which are long since gone. I was reasonably good friends of the dealer principal and shareholder of one such Brabus retailer, who told me the above.