I can't speak to the manifold issue (although my recently traded in 03 Limited did have this problem - and I never fixed it on the recommendation of my trusted mechanic ... "just drive it!" were his exact words ... someone else's problem now).
I did send Toyota Canada a detailed email regarding the safety implications of my experience with a seized front brake caliper (another well-known issue).
They did not do anything about it (i.e., no financial compensation or the like), but at least I put it on the record with them. I also forwarded their reply to Transport Canada.
Only by reporting issues that concern us owners can change happen - such as safety recalls for problems that the manufacturers eventually have to address ... Takata airbags, anyone?!?