"The element fell right out" is one of the reasons I've never considered trying to peek inside a lens.
I had a Canon EF 17-35/2.8L (on which I got a really good deal used, because the model is known to be a bit soft, and IIRC parts were no longer available). I banged it at an event (a July 4th exhibition of the ship USS Constitution), the hood didn't soften the impact enough, I held my breath and didn't look at any exposed entrails. I sent it to Canon, with an explanation to the effect of "the front fell off", along with monetary tribute. The lens came back not only repaired perfectly, but calibrated to what might've been better than new. In my living room is a poster-sized print of a crowd photo taken with this lens, and all the great happy facial expressions reacting to something happening are clear and sharp.
This particular image was when I was learning photojournalism, had just left practicing fluffy stuff at a street fair (e.g., visually appealing image of vendor making candied popcorn), and the crowd I was in suddenly parted, to something newsworthy, and muscle memory kicked in.
I didn't try to publish it, because it turned out to involve a celebrity (who I didn't recognize until a real photojournalist told me), and I had a rule against shooting that, but it was a happy enough image that I had a print made for myself.
I've had a no-name 28mm lens apart a couple of times to clear oil off of the aperture blades. The old manual everything lenses are relatively straightforward to get apart. Be aware of the minuscule ball bearing that engages the detents in the aperture ring. It's spring-loaded, which might be obvious to you, but wasn't to me the first time I took the lens apart.
In my experience it's never "obvious" until it flies across the room :D
https://petapixel.com/2016/02/09/this-teardown-of-a-sony-e-m... (blog bait summary — but with a bit more text)
https://www.youtube.com/watch?v=g9umAQ1-an4 (the actual video)
First, hepa filters tend to block flow of air A LOT. Lens designers strive to get lenses to focus as quickly as possible. Any blockage of air would necessarily make it very difficult for the lens to breathe quickly.
Second, dust particles in the lens do not affect the image nearly as much as you would think they do. Just look at this pic: https://www.lensrentals.com/blog/2008/10/front-element-scrat...
The dust that gets inside from breathing while zooming rarely affects image quality to any meaningful degree. Excessive humidity can lead to fungus growing on the glass though, which really can ruin your contrast. It's normally good enough to keep your lenses in a box with some silica desiccant during summer to prevent that.
And if the seal fails then you'll get a lot of dust inside.
Despite Sony's insistence on DRM they make some very repairable hardware. For instance, it is dead easy to replace the controller switches, battery, and other parts on the Playstation Vita where the flex cables are very well routed.
I think it's a bit more glue than I like, but still reasonably serviceable for something with small parts in a restricted space. About on par with a Toshiba laptop, not as good as a Thinkpad (based on my experience with now outdated hardware repairs).
Or if you're a Nikon fan, here's their teardown of a Nikon flagship a year later. Note that this camera wasn't suspected of exposure or abuse, so not really a comparison but I'm fascinated by how modern pro cameras are built, their weaknesses, and how they may or may not be serviceable.
I couldn't image doing the same thing with a current lens that also has all those electronics in there.
I've taken a lot of stuff apart in my days, but never an expensive camera lens. I've owned, just off the top of my head, a 70-200 f/2.8, 50 f/1.8, 85 f/1.8, and a 105 f/2.8 macro lens back in the day when digital was just starting to catch on.
There are times where I miss photography...I always assume I'll get back into it at some point.