MX5 NC Steering Rack

Hi guys I need a new steering rack for my NC 2010 3.5.

Looking for a second hand one and many are coming up with different part numbers at the end i.e a different letter at the end.

Just wondering if anyone knows the exact part number and if there have been any revisions etc, or whether one rack fits all from 2005-2015.

Cheers

The letter at the end is just the supersession, you can always fit a later letter but not an earlier one.

Thats worrying - how many miles??