Found this during a rear shock change on a members saloon...
Once cleaned, it looked like this...
Fortunately the inside showed no sign of corrosion...
So outside was treated with Kurust, then Some Dinitrol corrosion resistant paint, before subsequently being liberaly coated with brushable seam sealer and finally a good coat of matt black paint just to finish it off.
Here after the Dinitrol...
Basically, if when fitting saloon rear shocks, you find any sign of rust here, be sure to investigate it... On this car, the right hand turret was perfect, so was simply brushed clean, given a coating of seam sealer and painted matt black. If in doubt, remove the boot side carpets to double check
The mounting turret, as seen from the inside was clearly a separate piece to the inner wheel arch, which could readily be removed for repair/replacement... is part of original repair assembly Inner Wheelhouse Right, 9117705; and Inner Wheelhouse Left, 9117704.
The actual turret appears to be sided, but only subtly, so if you need a left one, then the right hand one from a donor could perhaps be made to work...
This issue shouldn't affect the estates in the same way as the shocks are mounted inboard on the chassis rails rather than within the wheelarch.