Originally Posted by GreenMonster
Get an engineer, period.
I agree with this. I think this is the best statement made on the entire thread.
Call a local SRW supplier and find out who they recommend for an engineer. Many engineers work freelance. So you can just call them direct and pay them a nominal fee to come out and assess your wall and make recommendations. They will do a series of tests, analyze your soil, drainage, compaction, etc. and then they'll be able to make much better recommendations than any of us here can.
It would have been nice if the wall had been engineered when it was first installed. Then it probably wouldn't be failing now.