A number of folks have reported C41 problems with streaking and color spots, and I had these problems myself. They went away as soon as I started using a stop bath. Today I still process at 38°C but never without a stop bath. I use self mixed Agfa 304 as stop bath, which is a cheap acidic fixer that both stops development and takes some fixing load off my BLIX.
If that is too much fuss, any Acetic Acid or Sodium Metabisulfite based stop bad will do the job. PhotoEngineer recommends against Citric Acid, so be careful if you use commercial stop bathes.