In addition to what's already been posted,

Rust is like cancer: left untreated, which apparently is the case in the car you describe, it can become a systemic problem that leads to demise. Unfortunately, the 140 series is underappreciated at the moment, so if you buy it and you do have even moderate rust problems to remedy, you can easily end up with an overrestored example. That's fine as long as you burn with a passion for the model you've sunk the time/money into. I'd get it up on a lift and go over it carefully. It also sounds like the current owner isn't meticulous about engine and clutch maintenance. Neither is a good sign.

For reference, I have a '69 144s, 88K original miles, B20, M40, zero rust, no dash cracks, all original except the radio and carbs, needing only some work on the seats. I doubt anyone would offer $4K for it if I were to put it on the market.

Good luck