For me, it depends on how much I have been sewing.
There have been some lengthy times - up to 6 months and more - where I couldn't sew. Then there have been times I think the sewing machine and I are one entity and wonder I don't sew in my sleep.
I do my own oiling and basic cleaning. I do take my machine in on what I feel is an equivalent to 1 year of use.
ali