Fun Fun Fungus - Cleaning fungus from a camera lens

I have a lens that I used back in the 90's and very early 00's with a film camera and now that I've finally got my hands on a DSLR I wanted to use the lens with that. The trouble is if you leave a lens sitting around doing nothing for 15years there is a good chance it will grow fungus. This completely degrades the image so as to be unusable. Having figured out it would cost the same or more than a secondhand lens to fix I decided to have a go at cleaning it myself.
I have had mixed results.
I've managed to disassemble some of the back of the lens and get at the element that has the fungus. Unfortunately it's in a subassembly that I don't know how to take apart. So I've removed some of the fungus using an ammonia and hydrogen peroxide bath but there are still some bits I can't get at.
Apart from my bedroom smelling like ammonia, there also remains the minor problem of putting it back together… What could go wrong?