Right folks we have been here before.
https://www.fiatforum.com/croma/263259-steering-rack.html
Following on from this thread I have discovered the following from
eper and t'internet.
There are four types of Croma steering rack:
51753895 is for the 2.2 Petrol
717440550 is for the 8v Diesel
717440551 is for the 2.4 Diesel
717440552 is for the 16v Diesel and the 8v diesel if fitted with ESP.
All these racks are also used in the Vectra C and Saab 9-3 but I can't find any way of cross referencing the part numbers.
However if it turns out to be the internal ball joint I have found that there is a tie rod repair kit available from TRW and Lemforder.
The tie rods are the same for both sides of the car irrespective of whether it is LH or RH drive.
The tie rods for the 1.8, 8v diesel and 16v diesel are common, the 2.4 has a different one.
I cannot find a UK company that supplies them, but they are available from a German company.
The Lemforder one for the petrol and 1.9 diesel is £23.83 plus £13.92 shipping
http://seekpart24.com/lemfoerder/axial-joint-tie-rod-2772701?c=100198
The TRW one is £16.26 plus £13.92 shipping
http://seekpart24.com/trw/axial-joint-tie-rod-jar958?c=100198
Fitting them is a piece of cake for any reputable garage and should take no longer than an hour plus re-alignment.
Got to be better than £900. Simples!