I'd just clean it really well with soap and water and then see how it looks, If you don't see many black spots or bad spots and the seam sealant looks good it should be OK.
If you want to recoat it I think any RV roof coating product should work fine.
Last summer I actually redid the slide membrane and it wasn't too difficult. I did it mostly out of interest to see how things were under there and redo the flashing seals. Here is the video -https://www.loveyourrv.com/alpha-systems-superflex-roof-installation-replacing-rv-slide-membrane/

I'm doing my roof in a few weeks and hope to do tops of both slides as well (if my three gallons of Dicor product takes me that far.) I'll let you know how it goes on the slide roofs. -RP