Check what filters your fav IEMs use (diameter, ect.) and buy some replacements of aliexpress or amazon, they are very cheap.
Corrosion can, when noticed quick enough, usually just be "scraped away" and you are good again. The muffled effect really just comes from earwax getting behind the filter, as long as this isn't extreme and enters the shell you can usually just replace the filter and they feel like new.
@asunoaim yeah they just either turn muffled on one side overnight or miduse, and my earwax are more wet than dry and they just corrode LOL, i tried cleaning the filter when it happens but they just get muffled a couple days later and i cba