It depends. If the quality of the panels is similar to Temu products and not design with any repairablity in mind, then even with almost no labor costs, it still might be more cost-effective to simply replace the entire thing.
I was thinking about this too. There are tradeoffs around repairability. As an example, if you're expecting the unit to live in a wet environment it's not unreasonable to consider potting the circuit boards. This makes water ingress as a source of failure significantly less likely, but also has thermal effects (heat can't radiate very well through a block of silicone) that can hurt the overall lifetime as well as make it almost impossible to repair.
The most likely part to fail is the charge controller. That's got enough brains and parts that are ultimately likely to fail due to something like a bad capacitor. Next up is the batteries. If they are lead acid, then simply letting them under charge or dry out could have damaged them. Then the transformer/convert would be my next guess. It's got the right set of parts to go wrong. Panels is the last thing that might fail. They have no real parts to them, just cells and wires. About the only thing that could go wrong is if the wires somehow corrode (someone removes or scratches off the protective layer). Otherwise, the panels will likely just lose efficiency over time. They'll still generate power, but like 70% of their new condition.
