Aidan;
That "Flame Trap" is a standard part of the Oil Trap Assembly...it looks fine, and it gives any oil droplets lots of surface area on which to precipitate out, fall back into the Oil Trap, and make their way back to the Crankcase...I'd leave it as it is after cleaning the OT with mineral spirits.
The "one-way valve" is aka the PCV Valve...it has a preferred attitude of installation, because of the low force spring applying the force on the internal shuttle (should/must be vertical!)...that is why it is typically located right above OT in the B18 installation.
PCV Reference:
https://www.sw-em.com/pcv_diagrams_and_notes.htm
Cheers