Removing KL4 Donut

Having just got my hands on my first Lux V light (KL4 on a FB1 body)
and constructing my first TW4 (yeah I know i'm a bit behind)
There's only one problem, there's a donut hole in the beam, it's not too noticable but I want to get rid of it.

I've ran a search and I've found that i need to open the head up by boiling it in a ziploc baggie, which I can do.
After i've got the head open what do i do?


Do I have to cut down the reflector or do I shim the reflector to increase the height? Will a O-ring be enough width or will i have to experiment?

Thanks

quokked!

***UPDATE***

In my fever to get rid of the donut I seem to have killed the circuit
some water may have got in
Cheap Ziploc Bags, u getta what u pay for :laughing:

Now in every failure there is a opportunity so what should I get this head modded to?