I take mine in anywhere between 1 to 2 years, and again if there is a problem. When I bought it new it went in 4 times in 5 years at no charge. Not so often now. I take of the top plate and clean all I can reach, and oil what I can/needed as directed.
The new babylock I am waiting to come in with go for it annual between 12 - 18 months depending on use.