I can't remember where you're located. Brisbane, was it?
Here's parts in some kind of common order of failure. Print this list out and cross the things off as you fix them.
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Radius Rod (Strut) bushings - replace only with rubber!
"
americanautos" price $25.75, P/N
SBBK4
Idler arm bushings - Urethane one end works nicely. Urethane both ends makes less durability from what I've noticed.
Super-Pro part
SPF1414K Not sure on price.
Pitman arm - price varies greatly by origin. Some are rubbish. Try for a genuine Ford one. Repro is about $50 power steering, $40 manual steering (the parts are different). Add about the same again for genuine.
Tie rod ends - Genuine Ford Oz, American/Canadian or Japanese are all pretty decent.
"americanautos" price at :$29.95 inner (P/N
TE549L), $19.95 outer (P/N
TE548R)
Upper ball joints - Look for greasable ones if you can.
Price varies greatly by where they're made. Generic part number is
BJ94 and can cost from $20 each, to $50 or so. Easy to find at parts shops.
Spring saddles - Urethane is good here, too.
Super-Pro
SPF0335K for the pair; about $120.
Upper control arm inner bushes - Urethane again.
Super-Pro
SPF2293K. I have never replaced these on an XF, so check with their tech line to see if special equipment is needed. Probably about $120 total for both sides.
Anti-roll bar "D" bushes. Often you need to buy
new saddles to suit the replacement bushes. They're about $12/pair, and should come from whoever makes the bushes - either Nolathane or Super-Pro. Two bolt spacings are possible - check your car first. The actual bushes in urethane are about $15/set.
Anti-roll bar end links. I really suggest rubber, but apply a good dose of
Castrol GRR grease to wherever rubber meets the metal. any other grease will roth the rubber. Grease is about $12/big cartridge. You will have to go to a Mustang spares importer for the rubber end links. I believe Ford stopped supplying them finally.
Lower control arms - best replaced as a complete unit/pair unless the ball joint has suffered extensive damage for some reason. Not sure where to source, or approx price but not cheap.
Last on the list is the
steering flex coupling. It's the rubber disc just next to the steering box. Rubber fails slowly, but urethane gives a more direct feel. They're each about $55 and fairly available. You need to tighten them with a spacer inserted, which you then pull out after torquing. This part will make the difference between the steering binding up, and working smoothly!
OK, there's your homework. Report back when it's sorted.

No matter what your springs may be, all of this applies.