Hi,

eh... I have attached an image to illutrate... downloaded your model will upload the modified right after this message...

1. even thou you have merged it is still 2 objects... or the part where you have merged... I have X-rayed shaded it... the dark part between the 2 red arrows should have looked like the one side with the Yellow circle...

the faces also looks kind of strange... the blue circle and the extra red circle...

2. but I delleted the whole side... and then used fill hole...
(Edit Polygons... --> Fill Hole)...

3. which fille up the side... however the face of the side still looks a bit strange in my opinion... but that is proberly because it isn't divided...

this is also the file like I will upload...

4. I splitted the side and got the faces to look like this... I don't know if that's an idea... otherwise you will have a file like with "figure 3"...

regards

Strarup