Alright, so I finally figured it out. Oddly enough, there wasn't anything else holding it down. BUT, it took an enormous amount of pressure to pop it off. I big prybar over the cylinder to the back of the intake block, and a hammer claw under the front. Prying on both together I was finally able to pull the ******* out. To my surprise there were not extra clips or screws anywhere to be seen, just some insanely tight friction fit I guess. The boot was not happy about this forcing off but it survived. I did damage it a little trying to put it back on however and forcing it back on the same way. NO DICE. This just doesn't even seem possible and I was really putting a hurt on my boot, I've lowered it's life I'm sure especially where I can see visible damage where it was being mashed against the cylinder flange. It still holds air but not for as long as it would have. Ultimately I had to modify a few things to make it work.
Pic 1 shows the tools that were in my hands when I finally got it off and their relative positioning. The business end was prying up on both sides of the white intake block at the same time. The hammer under the what looks like a cylinder that pokes out on the top front and the pry tool under the recess at the top in the back.
Pic 2 shows my surprised view when it came off, nothing there!
Pic 3 shows the modified ring with a few mm or so taken out and the stihl 290 boot clamp over it. (there was some fighting when I slipped the intake block back on getting the stihl clamp in between the block on the rear but it was ok. I could have probably tightened it more first and had less trouble.)
Pic 4 shows how I shaved part of the back side off so rather than having to try and shove it in top down you can instead just slip it back onto the boot & pull it through and not have to fight the hell out of it. I had to keep taking more off until you can basically just bypass the notch in the intake block on the back where it would ride over where the screws go. I had to make it flush with the deepest part of the original groove basically until it could then just slip right past. Doing it this way you can make sure the boot is on the cylinder nice and the impulse is in there good and not have to mangle and reef in it to try and pull it through ridiculously while you mash the intake boot back down. Its a horrible frigging design I think and it's not even remotely serviceable that way without removing the entire cylinder and that's just friggin silly to simply replace the boot or put a clamp on because the darn factory white ring doesn't hold for s**t.
I have no idea what others might have done that have worked on these saws before but this is what I had to do and what worked for me.
With the clamp tighted to where the ring just touches edged to edge again it runs great and doesn't fluctuate anymore, so thankfully I didn't do it all for nothing and I guessed right! haha! (At least I hope so. I only did about five cuts with it but it ran nice and wasn't turbo'ing off into the great blue yonder randomly like it did before after the first cut.) So hopefully it's fixed. Gonna probably do the cat muffler delete and leave it alone from there and enjoy the nice running saw. I still thing the design is butt though and I don't like these that the cylinder mounts directly to the case either, I'd rather have a clamshell bottom and mount that to the case. I get it saves them parts/money but I don't like it. I was looking at comparing the stihl 250 to the husqvarna 435 last week and noted that the husky is designed that way as well and there were two little metal pieces that had to be just right on top of the seals when you put the cylinder back on and I was like wow, no thanks, I'll go with the regular clamshell MS250 for sure I guess.
Anyway, that was my experience here with the CS 352, hope that helps somebody in the future because I sure had a hell of a time figuring it out! Heh. I had to do a little modification to the 2511T I have too, that 3/8 stock bar they sell it with is chatter city and it sucked hard on that little saw. Modded a stihl bar onto it in .043 and it was night and day. I didn't want the 1/4" because its a little too small for my taste and I jump chain too much as it is on other saws so the .043 is a better choice for me. I posted pics for that in another thread as well if anyone is interested.