E34 Steering pump woes

Hi all,
I need some help as I believe the dealer is misdiagnosing a problem.
The car is a E34 520i, '94 with 130,000 Km, I'm in Spain.
A week ago I left the car at the BMW dealer to diagnose an intermitent metallic
noise in the front right of the engine, most noticeable at idle or low rpms.
They told me that they need to replace the steering pump at a cost of 340 Euros plus labour. The only available pumps from BMW are refurbished ones (I verified ETK).
When I went to get the car it was doing the same noise, after some discussion with them they kept the car to check it again and told me that the replacement pump is also bad. I looked at the original one and turning it by hand it had no appreciable slack or sticking and no trace of fluid loss. BTW the steering was working just fine.
There are any other failures apart from the pump that can cause such intermitent metallic noise?
Are refurbished pumps from BMW so crap?
Thanks in advance
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Sorry I made an errror, the noise is in the front left side of the engine.
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Yuki wrote:

The dealer should be looking for a restriction in one of the hoses. NOT uncommon as the cars age. There is a restriction built into the output hose from the pump that can get partially plugged up. This causes the pressure in the pump to go WAY up and the pumps make noise when this happens. The pumps themselves rarely fail. You may also want to have them replace the PS reservoir. There is a filter in the bottom that cannot be replaced by itself. This plugs up with time/miles/kms - and causes starvation of the pump.
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Thanks Don,
I was thinking also in terms of some problem with pressure regulation or bomb cavitation as after replacing the pump it still makes noise.
I made them also to replace the water pump (original), under their suggestion they are replacing also the thermostat.
Do you suggest to look for something else?
Thanks again.
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