Originally posted by xjjohnno Removing that name plate will allow you to remove the first 2 elements and access the front side of the 3rd element which seems locked in from the other side. I had to clean up my bargain 50mm f1.2 and had a dented filter ring to fix first before being able to remove the name plate and accessing the glass. Fortunately all the fungus was in the first 2 elements so I didn't need to access the lens from the rear.
I think what the repair shop is having trouble with here is the small rings used to hold the lens elements together into a group. These have spanner slots so you don't need a friction tool and are usually no trouble. But they are aluminum threaded into aluminum. Aluminum has a very strong oxide and the oxide can effectively bond the rings together. It is extremely frustrating to have a part that maybe cost a nickel get in your way like that. That probably explains this destruction:
Anyway, I would vote for attempting to kill the fungus in place. If the problem is as I describe, the shop is right, and the only solution is finding a replacement ring. That may take a while. You can use the lens in the mean time. Take photos of the fungus, keep it dry and monitor the progress.