Ace,
If you are using the new Z5 (white bottle), and get the smearing, go and mixup 1/2 cap of Z7 and 12oz of distilled water in a spray bottle. Spray the effected area, then wipe off. No more smears!
Don't use Z6 to try to remove smears, it just moves the Z5 around. Z6 is best once Z5 has cured well enough and is ready for your next coat of Zaino.
When I did the SC430, it was Z6 B4 and after each coat and on the applicator pad which I changed to a smooth foam type as the terry one just absorbed too much. Applied really thin so it's had to see. Came out fantastic. A lot of problems with and sealants, Zaino, Klasse, BF, etc is the lack of proper prep so that no oils or silicone is on the surface of the finish. This is why it also looks somewhat plastic, the oils under it make the sealants look obscured.
Regards,
Deanski