The Rover 75/MG ZT shell is a 3 series BMW in guise, all parts are bespoke BMW items ranging from the 3 to the 5 Series BMW's, the bodyshells were zinc dipped, and as of yet are still to see any major signs of corrosion of problem areas.
The mechanics are a mix of BMW and Rover, the 75/ZT carries a modified rear wishbone setup that was adapted for front wheel drive, and this came from the 3 series.
If the ZT your seeing is a 180, it is still a V6 and is a 2.5L, with different engine mapping, the induction is the same as the 190.

I have heard that the top suspension on the 75/ZT can break.

If you ask Ralph (EMS Ltd) he will tell you the common faults..........there are also 'flooding' problems with regards to drain channels being blocked too iirc.

Have you thought about joining the http://www.the75andztclub.co.uk/forum/ to gain some knowledge of the car........

Jim