Just as Said above, from personal experience the factory protection and seam sealer from the factory is pretty crap, I'm restoring mine and when your under and having a close look there's panel joint's where the bead has completely missed the panel joint's!!! Leading to a hole forming. I'v had the car now for a while and during stripping the doors noticed that down the front edge the factory sealer is missing in places, I'll post pics later to show you what I mean.
The rear arches are the biggest ball ache, on our British Hondas the inner skin stops back in from the outer skin on the rear and is sealed with a bead of seam sealer but the Teggy's are both flush and between spot welds have 2-3mm gaps where the water soaks in, very bad in winter as the salt water doesn't dry at all hence the rust starts.
On my car I have seam sealed the rear arches then painted with 2 coats of Jotun 2 pack paint as well as the whole underside so should stay fresh for a long time, so my point being, if you get a fresh import and spend time stripping sealing and protecting vulnerable parts then rust should remain a distant problem for at least a while longer, the same as a normal British manufactured car, but left unprotected or a poor undersealing job then it's just a matter of time before the rust sets in