Hi Jose, I have never tried to paint the swirl on the spinner before, I have always had some in my spares box or with the decal for a particular model; so I haven't had to try.
As to Solvaset, yes it is strong stuff, sometimes on some decals you need it. You can "thin" it down by adding a little water to some in a small cup, to lessen its strength. I also used Mico Sol decal softening agent, which is quite useful as well and not as strong as Solvaset.
As for the swastikas, I recommend going to someplace like Squadron online, or a local well stocked hobby shop and seeing if they have any swastika sheets. These are produced in various sizes for various types of German aircraft. If all else fails, I can send you a couple swastikas from the U.S. for your Junkers 87. Take care, Russell