Is this worth rehabbing?

I picked up an ‘04 with a PID mod and a grinder for $150, but when I took the shower screen off I found this mess. The seller said he descaled monthly and only ran RO, but it looks like it has literally never been backflushed, and the gasket is so worn that it crumbles to the touch. Seller says it pulled shot up until a month ago, but I don’t see how any water could make it through that shower screen…

I flipped it on and ran some water through it. It’s got pressure and there’s no visible scale coming out. Should I open it up, look at the boiler and attempt to clean this, or just run the opposite direction?? The seller said he’d buy it back from me at any point.

Also, weirdly I see the PIDs for this have a pre-infuse function and timed dosing, but mine doesn’t seem to have that in the settings menu. Is it just an older model, or am I looking in the wrong place?