I think we’re taking about OG Defenders here so pre 2016, hope I’ve understood that right?
TL;DR: For any age - Head over heart always, be sure you’ve costed the running costs properly and put on top as it’s more than you think, if it’s a newer style one rust won’t be an issue otherwise it’s part and parcel of owning one.
I’ve always wanted one too @Dan5 but for a few reasons it’s never quite happened. I’m by no way an expert so these are considerations…
Firstly, head over heart. Especially important, there are a lot of upsides of owning a Land Rover and a defender at that, but there’s also reality. So the cold decision is especially important here.
Secondly, price. These have gone up the roof astronomically and have essentially become classic collector cars. You will struggle to get a truly decent defender (condition, mileage etc) for sub £20-25k unless you make a compromise somewhere.
Things to consider/watch out for
Defenders were always seen as a tinkerers car, so unless you’re good mechanically you will become friends with the local mechanic and very soon.
Defenders themselves are decent enough bodywork wise but it’s the chassis as you correctly note that’ll have the bad news. Mainframes, body connecting bolts etc. If it has been “sealed” that might mean it’s been cared for, it might mean it’s rotten AF - literal poking with a screwdriver or similar is the only way to know for sure.
It will get stolen at some point in its life, so invest in a seriously decent alarm and prepare for the worst.
Running costs. I used to own a 2017 Discovery Sport and that thing was unbelievably expensive to run and maintain. It’s not just the purchase price that you need to think about.
Assuming the above doesn’t make you go and invest in a new one or even an Ineos Grenadier, then unless you are very deep pocketed you will be resigned to the world of Facebook marketplace or private. Usual rules (no V5, price too good to be true, etc etc) apply here.
They do, if well looked after go for miles and miles, I’ve known many defenders go round the clock twice.
Good luck!