ABS Pump

[funkmiester]

having had a warning light and a code for low brake fluid pressure, it was clear the ABS pump had slowly given up the ghost at 212,000. A used/replacement has been procured via A8 Parts. Just some advice. The pump is in 3 pieces, the control module (black), the manifold block (silver) and the pump which is the black cylinder. If I have low pressure I assume it is the pump.
I have 3 options:
1) Split the pump off and replace the pump alone (If I do that does the system need bleeding?)
2) swap in the block and pump and retain my control unit?(in case of any compatibility issues, my replacement is from a 3.7 mine is an S8)This will require a full bleed of the system
3) Swap the lot?
Apart from a low pressure warning light the system was in perfect working order.
Thoughts and advice on a postcard please.
Many Thanks.