Change it everytime. Cheap compared to an engine.
Are you changing the oil yourself? Topsider or other way of sucking oil out of dipstick?
Is the filter on the top of the engine or the bottom?
Also, loose the K&N filters. They will screw up MAS sensors over time. Read -- $$$. I believe your model has a MAS. The very thin hotwire that reads air flow gets coated with oil from the K&N and then you replace the MAS.
K&Ns work well on small airbox designs without a MAS. MBs have large airboxes and do not need them. Use an OEM filter.