I had the same problem a few weeks ago, The wheel got very stiff at around 45 degrees and was hard to get back straight again, Fluid was fine, Belt was fine, No odd noises from the pump
The solution:
I was told it could be corrosion debris in the universal joint, This is the shaft that runs from the steering wheel to the steering rack, it's a round bar with 2 knuckle joints, These were the problem, You need to find some duck oil, It's like WD40 but will not form a seal and lets the !Removed! out, It's made by Swarfega, Spraying is messy and it stinks if it hits a hot exhaust so I filled a syringe, Apply liberally to both knuckle joints, If you have scrawny arms like me you can reach down from beside the air filter, Once it's soaked in a bit start working the steering lock to lock, Hopefully things will get easier, Keep applying oil and working the steering from side to side, you need a good 20 minutes of this, maybe half an hour and don't skimp on the oil, All been well by the end of it you can go lock to lock with just one finger, I've not tried with WD40 or any other release spray so I can't really recommend them but they will possibly work, It's a cheap and easy fix, My car is 15 year old with quite high mileage and it's the first time I've had a problem with steering, I'd not noticed how bad it had got but it's been fine since and drives like new
