.....or, designers make it difficult to change or seal it completely so that many miles and years later you will be paying for a new transmission!
I wonder about that, myself.
Change the fluids out regularly if at all possible!
+1.
I don't think any transmission sump strainers will catch anything smaller than 40 microns (find posts by our resident transmission builder
funtown89; he has not been on board for a while, but the information he has posted is very informative).
That said, the ATF becomes a "reservoir" for holding the
entire spectrum of wear particles until the next ATF change. Friction material from the clutch packs, metals from bearing surfaces as they wear, metals from the meshed gear sets, metals from the transmission case (for all those linear valves that reside in machined bores)...it adds up.
Jimbo66 is right: the only way to remove that stuff is to regularly change the fluid.
Man, I don't know what "super substances" are purported to be in modern ATF's where a manufacturer can claim a "lifetime fill", but when it comes down to basics, all ATF base stocks are manufactured by only a handful of producers in North America. Additives for anti-foaming, bearing surface friction modification, dispersants, detergents, viscosity stabilizers & improvers, and clutch surface friction modifiers are included to make it work with a particular line of vehicles, and then it now has a name, or thus a specification (GM Dexron III, or Honda ATF-Z1, or Toyota ATF Type T-IV, etc.).
If you are a track guy and use the excellent Red Line Racing ATF (Type F), it doesn't have dedicated clutch surface friction modifiers. I noticed they changed their wording to
"Similar to a Type F fluid, featuring even higher viscosity and no friction modifiers". It is no longer a fluid that
performs like a Type F with no friction modifiers (my emphasis added). Their engineered synthetic base stock, plus the remaining Red Line add pack, gets it genuinely close enough.
That said, even if the additives package lasts the life of the vehicle (which I very sincerely doubt it would), without a highly efficient and effective replaceable filter, we have no choice but to periodically change fluids. Besides a Magnefine on our Gen 2's, I also change that little spin-on in-line canister filter periodically (p/n 25450-P7W-003) and its associated O-ring (p/n 91301-P7W-003). Because I do the 15,000 mile single drain/refill method, these get changed every third drain/refill.
I've started opening up my old Magnefines after removing them; their internal magnets can be re-purposed as
awesome refrigerator magnets.
OF