I use "simonsays"(yes I know thats not the right name,but Im sure everyone knows what I mean).
I mean the original wax not the "simonsays" carshampoo with added wax,ultra easy to apply "simonsays polish for metallic finishes" or similar.
1 application per year does me, then regular garage pay for your wash runs.
If its set up properly there is a little tempory wax in the final rinse .
I allways use the final rinse of the cycle from a distance in a "mist spray", dont use it as a final ooh I missed a bit power blast..
Tar spots are the worst,.If you leave them for any length of time u have to use neat petrol to get them off and then wash car and reapply your "simonsays"
btw what is it about new cars that attracts flies
They leave "fly poop", I kid you not.Its like a very weak tar spot .
I dont like to link anything much on site now, but if you google for long term reports on the Meg III, you will see the guy is real keen on an instant long lasting super wax.