It sounds as if you may have had a viable claim. However, it does seem like you have wait beyond the statute of limitations for the federal Family & Medical Leave Act. I don't think anyone can be done under these circumstances but you should consult a local attorney as you may have other state law claims available.
4 years is well beyond the statute of limitations for bringing an action based on these facts, but you may want to contact a Michigan employment attorney to discuss whether there is any possibility of any issue operating to toll the statute in this matter for any part of the years since the event.
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