power steering pump keeps going down

Ok so 200tdi Defender 110 after 150000 miles power steering pump goes down so system is flushed and replacement pump is installed. This goes down after 600 miles so the system is flushed followed by a new reservoir and a new pump. This installation lasted 1500 miles and the pump just went down again.

Now I am wondering should I replace the steering box and pump and flush the system.

or

Should I install a new pump and put some kind of filter into the system before the pump

There is no roughness in the steering box when steering and my mechanic says that he would not usually suggest replacing the box given these conditions except that the pump has gone down so many times.

thanks in advance for your advice.

Was it a new pump or s/h?

Was it a good quality pump or one from ****part or similar .

Both were new pumps. Probably britpart as my mechanic swears by them ish. Both pumps have been returned for warranty claims the first one did not come back in my favor. So I guess that if the company operates a warranty scheme then they stand by the quality of their products?

What manufacturer would you suggest I should go with?