Yes, old C41 film does tend to have a darker brown base. Blixing longer doesn't help; what you're looking at is basically fog; I'm surprised you got anything usable from 10 year old ISO-1600. I've got some 2002 400VC and it looks really bad but you can scan a decent image from it.

Since you also processed some fresh rolls and they came out looking normal, your process is likely fine.