Airhead Airbox, R90S on an R90/6, should it fit?

I needed an airbox for my R90/6 and found one that was from am R90S. The guy who sold it assured me it would fit on my engine. See the pictures below..these are of the right side where the airbox meets the transmission. The right side as you can see does not match the transmission. It does however match the engine. The left side matches perfectly with the engine and transmission. The guy that sold me the parts seemed to know his stuff and says I have it installed improperly....but I'm sorry guy, this is installed correctly and does not fit. Does anybody out there know what might be going on here?

Ummm, he's right.
They are all the same fitment from 1970-1979 until they went to the square flat air cleaner and even then they all interchange.
It isn't always gonna be seamless.

But this is a solid 1/8 inch off, like the base is just not wide enough. Have you seen this before?

Take the box back off and put each half down on a good flat surface, thick glass etc, and make sure it's square, ie, no one has modified it with a grinder or file.
I have seen some that sit just a little different than others, but it ain't rocket science, it's just an old BMW.
Why did you buy this? Was it because of the holes in the back?
Or did you just not have one?

I needed an airbox because mine was broken where it attaches at the right transmission stud. I put up an ad looking for a new one and lots of offers came in. My broken one had the holes, but they were drilled by hand. I don't know why i bought it, the price was right and I was use to looking at the holes I guess.

Anyway, I had thoroughly checked this thing out and it looks perfect, not modified in any way. the 2 halves mate well, and as a pair they match the engine and transmission very well, except for this one spot. I can understand variations between castings and such, but this is really way off and doesn't seem like BMW would have left it this way. I am just confused by it.

Could my transmission be something different?

Make sure you have not over tightened everything and lightly tap on it with a rubber mallet to reposition it. They are all the same shape and mounting style from 1970-1978 and 79 would work in a pinch. That's as good as they get