Uncle metal-detector, the thread you're looking for is here. Threads drop off the list if no one posts to them in 24 hours. They don't disappear, but the message list only has threads active for the previous 24 hours. You can set the "age" filter up at the top to look for messages back 3 days, 7 days, etc. You can also click on "add thread to tracer" above where it says "Reply to thread," and it will add the thread to you personal page if you're a member.