In all the mods I've done, I leave the middle one alone. It tends to stay put since it's not used to hold the ESC in place. The lower spreader can be tricky to remove. I usually heat the spreader a bit to make the thermal pad adhesive a little more pliable. Even then you have to be careful not to damage one of the FETs.
Ok... I got the slab off with ease after applying a some heat from a heat gun last night... I'll cut the new slab tomorrow and get some thermal grease for the reassemble.
If it comes off that easily with just a little heat, no wonder the pad doesn't hold during use since those FETs can get pretty hot. Don't know if you've seen this, but the pic below shows the proper dimensions for the new spreader plate when not using the thick thermal pads:
Yep... It was quite disturbing to see how easy it it came off when I used the heat gun... I saw your diagram before when I started researching on this mod... nice illustration. I have a small sheet of 3/16 aluminum
(not much thicker than 1/8) That I think will work just fine after some light sanding and polishing. I am not sure if we have the popular 'ARCTIC ALUMINA' in the island... so I will have to settle with the generic brands.