Repco is selling Meguiar's Ultimate Wash & Wax 1.42L for $18. This beats the best price ever by $2. Supercheap has it for $27.99(supercheapauto.co.nz). So if there is a SCA near you then get them to price match it(supercheapauto.co.nz).
The deal is part of their latest catalogue(repco.co.nz).
Tipoff to Hugh at OzBargain(ozbargain.com.au) as I suspected the AU/NZ deals would be similar.
Are you washing your car under the sun?
No. And thoroughly rinse off.
You probably got a bad batch or something. I have been using this for years and never had this issue.
Maybe you're using too much? Did you try a different dilution ratio and use less of the product?
If there is an issue with the way it's applied (not saying that there is), then most washes with wax in it will probably not work for you.
What have you switched to now?
I stay away from wash n wax combo. Am using Armourall car wash or Turtlewax car wash. Its usually $10 approx.
I highly recommend NOT wasting your money on this product at any price. It's the worse car wash I have ever used, as leaves soap streaks all over your paintwork and windows. You pretty much need to rewash it each time with a different product. I persisted for half a dozen washes, then finally binned it.