"As I said" vs. "Like I said"
Solution 1:
Like I said is much more informal than As I said, but the former isn't ungrammatical. In formal writing you may prefer to use as, but in speech or less formal writing like is fine.
Solution 2:
The increasing use of "like" pushing away "as" (expressing comparison) - especially in colloqial language - may be explained with the fact that the function word "as" has too many meanings.