power steering problem with ford mondeo 2001?

I have a 2001 2L td ford mondeo. The power steering fluid was leaking from the bottom of the pump I fixed this by changing the gasket. I've notices that at low revs the steering wheels judders, at high revs this seems better, the steering seems heavy at both high & low revs. I've checked for other leaks & can't find any. As an aside the subframe had to be dropped to replace the suspension on near-side just before the problem started