Replacement 40cm roof vent for an 05 Symbol?

Hi all. Has anyone ever replaced the 40cm x 40cm vent above the kitchen area for a different make? I'm looking at various vents online and I'd like to get a clear one. The closest fit is the fiamma crystal 40 but I've noticed that its only for a 39cm x 39cm hole. All the others seem too big. It's very close to a cupboard so it's a bit tricky to find a suitable replacement.

And yet it's called a "Crystal 40"?  

RogerThat wrote:And yet it's called a "Crystal 40"?  

Yes, it's weird, i know. The dimension drawings show a 39x39cm hole.

I've seen the Fiamma used to replace an mpk so don't know where they take the measurements from but should be no problem.

After much thought, I'm just going to replace with a brand new MPK vent. The fiamma crystal also requires drilling into the roof. I'm just not comfortable with that. That's a whole load of new future potential leak points. It's a shame that MPK don't do a clear version of that old vent. They do a clear dome but it's a different shape and would clash with the little spolier.