Neighbor's Sewer Cleanout Is On My Property And It Is Causing Issues

Both homes were built in the late 60s. I purchased 4 years ago, he purchased 15 or more ago. He had no idea where his cleanout was, said he never needed it. My survey does not list his cleanout, does not list a utility easement on my side. Suddenly some type of sinking hole opened up on my side of the small yard between the homes. I thought the recent drought caused shrinkage of the soil and asked a landscaper to come in with fill dirt and fix it. Doing this job he found the neighbor's sewer cleanout and it's cap is broken, we "assume" this caused some type of disturbance from flushing or water cause some type of sinking. I made neighbor aware. We put a hold on the landscaping until we deal with this.

He does not want to pay a plumber, does not want to pay to fix it or move it and wants to cap it himself and the cover it back up with grass leaving it unmarked again. He told me I was welcome to pay a plumber if I want it fixed right since it's on my side anyway.

Legally can I make him move it at his expense? Can I make him pay to fix it because it's his? It is causing a large hole on my property, I'm afraid someone will fall so I want it done right. Property is in Florida. I will pay to do it right so it's done right but I also don't want to have to continue to deal with it and would rather it's not on my side at all. If I pay am I opening myself up to continued ownership/liability?

I am 100% certain it is his cleanout and not connected to my plumbing in any way as all my pipes were redone in the last few years and my plumber confirmed it. Also if he flushes, water shows up in the open cleanout so we verified it is his. Tried to give as much background as possible.