The DriTac will fix the problem, it better to call your installer but you can also do it buy your self. there is two kinds of kits one for engineered and one for solid, Here is a link that might be useful: dritac repair kit

Well I might consider painting the metal trim to match the color of the vinyl. But then I run into the paint scratching off. I think I might be to the point I do not really care about it being metal. I have it into laundry room and pantry and never really see it. Course this area would require a wider metal piece then those. Emagineer the tile deal will not work on manufactured home. I do not think I have any pictures of the house coming together at the seams. There is no drop off. They screw the two halves of the house together with a rubber gasket between which does not really show. Then they take the "Stuff" spray to fill any gap that might be left. Then it is smoothed and in our case now there is carpet over the joint. There is the metal strip that holds the carpet and I am sure it is nailed through the seam edge of the vinyl so there needs to be another metal strip wide enough to cover those holes when the carpet and strip are removed. Hard to explain.There is no gap or lowered area between the two halves of the house. I need to go up to neighbors and see how they bridged the seam because they also have vinyl in kitchen and living room which are open to each other. They researched it all half to death and really metal is the only option.This one from your link is about what it will look like. Schluter®-RENO-T It might need to be a bit wider than shown. Chris

As millworkman states, the 'fix' is new trim at the floor level. A finishing carpenter can do this for you. You could trim off the door frame and continue the wall trim in it's place. It is a very handsome look...but it is $$$. If that is not something you want to do, then go ahead and do a paint patch on the bottom of the trim and then ignore the gap. There is nothing you can 'stuff' in there that will be appropriate. Anything you throw in there will PREVENT a nice 'fix' in the future. You will make an ugly (but functional) situation worse. How bad could it be? It could be so bad that it effects both the hardwood finish AND the wall. It could be that bad. Just a paint touch out and then leave it alone. Anyone who is lying face down on your floor in your doorway saying "Dude! You didn't do the door right!" is probably having some other type of issue.

Even if they are tight now a 7" wide flat sawn white oak board will change in width up to about a sixteenth of an inch with seasonal humidity changes. You will certainly see that expansion and contraction over the year as appearing and disappearing cracks. You can also expect some cupping and bowing, depending on which way the growth rings are oriented. That said, if installed when very dry in winter you want them pretty tight. Overly tight and the wood will compress when it expands in summer leaving you with permanent cracks. It's also really hard to pull slightly warped boards flat if they are that wide, which makes installation a challenge. There are good reasons why people choose narrower floor boards. Wide board floors will, almost certainly, eventually have cracks-- it's part of their charm and character. Glueing them down is a bit of a fool's errand-- you can't stop the wood from moving and the forces involved are huge-- if the glue is successful you can end up splitting the boards as they move. You often see this on old furniture where cross grain glue goints were used.