I've made attempts to refurbish some reeds - and not others.  I've had very mixed results.  If you replace the o-rings and have no "joy", then you should look into replacing the tongues.  The tongues are not always commercially available.  Here's my experience...

 

Kinnaird:  Great success with refurbishing.  Contact the company for new carbon fiber tongues. They make a world of difference.  O-rings are 9mm ID with a 3mm wall.  (Sometimes called 9mm ID, 15mm OD, 3mm thick.)  The allen wrench seems to be 2.5 mm. 

Omegas:  The only thing I've ever done is replace the allen wrench with a 1.5 mm size.  

Crozier Fiberglass:  The o-rings are 8mm ID with a 2.5mm wall.  (Sometimes called 8mm ID, 13mm OD, 2.5mm thick.)

Shepherd:  I have experience only with the black and white originals.  The polystrene tongues would fail constantly. These are commercially available.  Polystyrene is well known to suffer stress cracking. I bought sheet polystyrene from a hobby shop and made my own.

Ross Cane reeds:  The tongues were readily replaceable, but I stopped trying after a while when the little rubber bands gave out.  Probably could replace with o-rings, but I haven't done it.

Ezeedrone:  no refurbishing attempted  (I've worn out the tongues on a couple sets, but just replaced the whole set.)

Best Tone (Caldwell): no refurbishing attempted

David Naill Carbon Fibre: no refurbishing attempted