It's quite possible that the combination of M030 springs and FSD dampers doesn't work as well as the standard springs in combination with FSDs - the dampers will be optimised for a given spring rate and can't be expected to work across a wide range of springs.
I agree with what has been said about replacing all four dampers at the same time. The fronts will be well worn by now and you will need four wheel geometry doing anyway, so you may as well have the whole job done in one go and have a set of dampers that should last for another 50K miles or more, rather than doing the whole geometry process twice.
Monroe dampers in the 993 application don't have a good reputation for longevity so alternative options are likely better value, especially when the cost of proper geometry setup is factored in.
I agree with what has been said about replacing all four dampers at the same time. The fronts will be well worn by now and you will need four wheel geometry doing anyway, so you may as well have the whole job done in one go and have a set of dampers that should last for another 50K miles or more, rather than doing the whole geometry process twice.
Monroe dampers in the 993 application don't have a good reputation for longevity so alternative options are likely better value, especially when the cost of proper geometry setup is factored in.