VERY heavy steering - need some advice
 

Hi all, i' new to this forum, first post.

My 2007 A4 Cabrio (Quattro 2.0L) has very heavy steering
About a year ago my mechanic replaced the rack with a salvage part which fixed a different issue but not the steering.
Then they replaced the power steering pump with another salvage part. Again absolutely no difference in steering.
I had a different mobile Audi mechanic check over the car and he checked the steering column joints but they are all fine.

1 strange thing that may help diagnose. one day last summer, it was very hot 34C, the car was sitting outside all morning and when I drove it the steering was incredibly light. Absolutely beautiful to drive but that only lasted for about 2 hrs and then went back to normal.:(

Canadian Tire just checked the steering and recommended replacing the PS Pump again.

2 Questions:
1 - Does this sound like the right thing to do?
and
2 - what parts to use? Its an old car that has cost me an arm and leg. Can I get away with a reconditioned pump or are there are any reasonably priced quality aftermarket parts worth trying etc?

Thanks all