Fibber,
First things first. This is no remnant from FS98 or any other flight sim.
The two locations in question, Abemama and Abaiang atoll were virgin territory when I went there and built the first add-on airfields on them for CFS2.
I guarantee you the locations were devoid of any of life.
And those two sets of hangars were never any part of any MR scenery packs.
These hangars have nothing to do with any random texture or APImacro that you will find sitting around someplace. They are most likely part of a scenery bgl file that is installed somewhere in some folder in your CFS2 set-up. The question is: where is this bgl file?
If it were me the first thing I would do is go through my scenery library and deactivate all of the active add-on scenery folders.
Then check to see if the hangars are gone.
If they are gone, then great. Then reactivate scenery folders one by one until they show up again.
The fact that your MB isn't working is problematic. Makes it difficult to determine whether or no the object is part of the GSL. If it were it would be targetable in MB. It would also be selectable in MB when the MBGSL editoor was active.
Another way to check would be to replace your current cfs2.gsl file with and empty.gsl renamed cfs2.gsl. Then open the sim and see if the offending scenery objects are still there. If they are still present then you know for sure that they are part of some add-on scenery bgl.
If they are gone then you will know that they are part of your currently installed gsl. And you could check in your current cfs2.gsl file, using GSKMan.exe, to see if there are any odd gls currently loaded that you don't recognize.
MR
PS: What it appears to me to be is some sort of first stab at a building of some sort. Either made using FSSC or perhaps GMAX or some other such 3d object making software. I am guessing FSSC. FSSC has this "advanced building" function where one can cobble together some half-axed looking buildings of whatever size you like. This appears to be something along those lines. It is more than likely part of some scenery bgl from somewhere.
The only question is, as I said, where have you got it tucked away? ;^)