As Gareth has asked, what colour is the car?

Which swirl mark remover have you been using? The one for PC use (Z-PC)? Or the non-abrasive one (Z-1)?

With the Z5, do you have a clear coat paint or single stage? Also, are you ZFX'ing the Z5 as this may make a difference as to how it finishes, especially now the weather is not as warm and generally damper....
I've noticed it makes a difference with the Z2 Show Car Polish for Clearcoats but, I'm not totally sure if it would make a difference with the Z-5... You never know though....

Finally... What Zymol are you using?

Cheers.
Alex.