Before you buy or possibly cut anything, you might also try to measure the Flattener Rear Optic dimension, just to make sure all that is being said in the manual "adds up" logically. Maybe you will find your lost/added 2mm there. According to what's said in the manual, that dimension should be 100-96 = 4mm.
You could measure it (
x) in the diagram by CAREFULLY measuring from the surface of the rear optic in the flattener to the end of the threads (Dimension
B in sketch below) and subtracting Dimension
A in the sketch below (the dimension from the end of the threads to the rear mounting surface of the flattener. If you get 4mm then that's one less issue to be concerned with OR if you get 2mm, then you have your 100mm overall.
If none of that works out, or even if it does, try to get in contact with other Esprit 150 users to get an opinion.
Best
JA