Slab sinking

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I would assume the base was not properly prepared. What does the concrete contractor say?

You can compact the ground until you are blue in the face and you won't reach 100 % compaction. The ground will still settle! The slabs should have been pinned together to eliminate uneven heights or seperation. Good luck, it will probably keep moving.

Was the pad professionally graded and compacted?

Humm I wonder how much it'll sink

This is existing from a previous owner

Can you just live with it? It might be pretty pricey to correct.

Sure a little uneven don't bother me. As long as it's not going to move enough to cause issues.

I have heard of polylevel something. I think foam injection that lifts concrete? Maybe cheaper than other alternatives?

A couple potential issues:
- The base wasn't well compacted and now it's compacting. As long as it stops and it isn't pooling water badly or otherwise causing problems, I would just live with it. If it gets bad or otherwise starts bothering you, yes, you can have a residential paving company come out and use injection to compensate for the sinking.
- How thick is the concrete? 4" thick and you can expect a 12x13ft flag to crack. There's a reason sidewalks typically have a 4-5ft joint spacing.
- Are there any signs of water washing away the base material? If yes, you need to stop that or it likely will continue to get worse.

I had my driveway raised by the injection method. Very happy with the result, and it was a lot cheaper than I expected.