Sealed fine but I didnt realize it was one time use until later reading on the forums. No leaks though, think im fine?

I changed my oil a month after I purchased my 2001 s500. I noticed the plug did not have a washer. It did fine without one so I would do a short oil change cycle and replace it if you are concerned.

If it's not leaking now, you're fine. No worries.

its fine. shop don't usually replace it when they do oil changes anyways

Some people overtighten the plugs and flatten the washer beyond 're-use' level. I believe this is why MB classified it as 'single use'. In your case it doesn't seem to have been the case. So as long as it's not leaking you're fine.
Brgds

i've flipped them over in a pinch.

It might weep a bit, but that should be it.

Thanks a ton guys! I was all worried haha. Perfectionist here I guess.