The ridiculous part was, it had just been over the pits. I'd copped a yellow sticker for a cracked windscreen I should have replaced, and the inspection had shown nothing major. But one item was a bent tie rod ( on the same side as the rust)--this was almost imperceptible, and the bloke who inspected it must have almost been looking directly at the affected area. It was only spotted by the mechanic who was replacing the tie rod. I got the phone call..."better come and have a look at this" . it was right through in numerous places on the lower corner of the channel, over about a length of 150mm. But only right in that corner, you could only see it underneath and looking out.
I had it repaired by the local panelbeater and put it back over the pits. Forward two busy years, and I get under it again and find the rust had spread, he hadn't got it all. Bigger repair this time, done properly, and replaced from near the top of the wheel arch downward sweep to the gearbox crossmember mount. Cost $2400 from memory.
At the time, the repairer reckoned he'd seen a few rust in the same place, when the AC drain was running into the chassis. All the rest of the chassis checked out OK on thorough examination, but it has always been obvious this old girl (395,000 now) has had a hard life.